create data table in r
We need to install and load them in your environment so that we can call upon them later. In my case, I stored the CSV file on my desktop, under the following … If you don't want to make changes in the original data, make a copy of it like mydata_C <- copy(mydata). "with = FALSE" is now dropped. data.table is the primary reason I prefer working in R rather than Python. The data.table R package is considered as the fastest package for data manipulation. 4963/creating-an-empty-data-frame-with-only-column-names-r tbdf <- data.frame(tbinput) where 'tbinput' is my input parameter of type table and attached with table 'sample'.Please help me out is there anything i need to include . The data.table R package is being used in different fields such as finance and genomics and is especially useful for those of you that are working with large data sets (for example, 1GB to 100GB in RAM).. Generating a Frequency Table in R . Introduction to data.table 2020-12-07. The output shows the resulting data has one row and ten observations. 5. Table () function is also helpful in creating Frequency tables with condition and cross tabulations. How to create frequency table of data.table in R? This data.table R tutorial explains the basics of the DT[i, j, by] command which is core to the data.table package. The main difference with data.frame is: data.table is aware of its … Course Outline. Pull first value of 'air_time' by 'origin' and then sum the returned values when it is greater than 300, 20 Responses to "R : Data.Table Tutorial (with 50 Examples)". It is also possible to select multiple columns using the list() function. Also, codes can become complex and inconsistent with dataframes. In fact, the A[B] syntax in base R inspired the data.table … Note that in data.table parlance, all set* functions change their input by reference.That is, no copy is made at all, other than temporary working memory, which is as large as one column.. To extract a single row of the data, we can use the syntax dataset[rownumber, ]. Thanks a lot to the author for making the subject so clear. We will use two popular libraries, dplyr and reshape2.This exercise is doable with base R (aggregate(), apply() and others), but would leave much to be desired. Hi,i have a table named 'sample' in spotfire with columns like col1,col2,col3,col4,.....,colm need to save as data frame using R script for that i am using the below statement. R can be used for these data management tasks. The possible values can be found on the page of default styling options.The default value display basically enables row striping, row highlighting on mouse over, row borders, and highlighting ordered columns. We need to install and load them in your environment so that we can call upon them later. They can be inspected by printing them to the console. No. Selecting Rows and Columns. And data.table wins. They will not, however, preserve special attributes of the data structures, such as whether a column is a character type or factor, or the order of levels in factors. Let’s see how to make a table like this. The middle value is 20. For example, creating a total score by summing 4 scores: > totscore <- score1+score2+score3+score4 * , / , ^ can be used to multiply, divide, and raise to a power (var^2 will square a variable). In this guide, we will use a fictitious dataset of loan applications containing 600 observations and 10 variables: Marital_status: Whether the applicant is married ("Yes") or not ("No"), Dependents: Number of dependents of the applicant, Is_graduate: Whether the applicant is a graduate ("Yes") or not ("No"), Income: Annual Income of the applicant (in USD), Loan_amount: Loan amount (in USD) for which the application was submitted, Credit_score: Whether the applicant’s credit score is good ("Satisfactory") or not ("Not Satisfactory"), Approval_status: Whether the loan application was approved ("1") or not ("0"), Sex: Whether the applicant is male ("M") or female ("F"), Purpose: Purpose of applying for the loan. I’ll start by checking the range of the number of cylinders present in the cars. Often the result of such a study consists of the counts for every combination. To create a new variable or to transform an old variable into a new one, usually, is a simple task in R. The common function to use is newvariable - oldvariable. In data.table: Extension of data.frame. Pivot tables are a really powerful tool for summarizing data, and we can have similar functionality in R — as well as nicely automating and reporting these tables. If a list is supplied, each element is converted to a column in the data.table with shorter elements recycled automatically. ), as this will make a complete copy of the input object before to convert it to a data.table.The setDT function takes care of this issue by allowing to convert lists - both named and unnamed lists and data.frames by reference instead. Tabular data is the most common format used by data scientists. Exercise. He has over 10 years of experience in data science. The join syntax is a short, fast to write and easy to maintain. The output shows that there were 38 applicants whose credit score was not satisfactory, but their loan application was approved. Note, that you can also create a DataFrame by importing the data into R. For example, if you stored the original data in a CSV file, you can simply import that data into R, and then assign it to a DataFrame. Value. data.table is much better than the other. Here is an example of Creating a data frame: Since using built-in data sets is not even half the fun of creating your own data sets, the rest of this chapter is based on your personally developed data set. Details. Yes. The output of the code confirms this exclusion. There are many benchmarks done in the past to compare dplyr vs data.table. This can be done using the convenience function that takes the form -c("col1", "col2", ...). Ltd. Table Function in R – Frequency table in R & cross table in R. Table function in R -table (), performs categorical tabulation of data with the variable and its frequency. Creating a data.table with R Introduction. %between%: This function allows us to search for values within the closed interval. Suppose you are asked to find all the flights whose origin is 'JFK'. Data visualization in R is a huge topic (and one covered expertly in Kieran Healy’s Data Visualization: A Practical Introduction and Claus Wilke’s Fundamentals of Data Visualization). The data.table package is an enhanced version of the data.frame, which is the defacto structure for... Data. We again created a table … In the example below, we want to compute the average income and loan amount grouped by two columns, Purpose and approval_status. The syntax for data.table is flexible and … No data, just these column names. CREATE TABLE test_results ( name TEXT, student_id INTEGER PRIMARY KEY, birth_date DATE, test_result DECIMAL NOT NULL, grade TEXT NOT NULL, passed BOOLEAN NOT NULL ); In this table, the student_id is a unique value that can’t be null (so I defined it as a PRIMARY KEY ) and the test_result, grade and passed columns have to have results in them (so I defined them as NOT NULL ). The most common and straight forward method of generating a frequency table in R is through the use of the table function. The first subset, s1, contains data for the maximum age of 76 years. R Tutorial: Data.Table. # Create two vectors of different lengths. Type the different percentages in column A. data is a vector that provides data to fill the array. Data frame is a two dimensional data structure in R. It is a special case of a list which has each component of equal length. For example, the line of code below will extract the entire vector of values for the Purpose variable. Creating a data frame. It is super fast and has intuitive and terse syntax. In R, a vector can be created using c() function. Saving in R data format. Here’s how. The data.table package provides a faster alternative for reading data with the fread() function, which is a fast and parallel file reader that can read local files, files from the web, and even string files. This section covers more sophisticated data aggregation techniques, such as performing summary operations within groups. dim attribute provides maximum indices in each dimension; dimname can be either NULL or can have a name for the array. It’s easy to select columns in data.table using the respective names. Choosing our Data Set to Create Descriptive Summary Statistics Tables in R For all of these packages, I am providing some code that shows the basics behind the tables and their functionality. Value. Let's start by loading the required libraries and the data. The syntax of data.table is quite similar to SQL. This article represents code in R programming language which could be used to create a data frame with column names. So we can ignore all the values that are lower than or equal to 10. In Part 10, let’s look at the aggregate command for creating summary tables using R. You may have a complex data set that includes categorical variables of several levels, and you may wish to create summary tables for each level of the categorical variable. One Variable Data Table. The structure of the resulting data shows that it is both a data.table and a data.frame. You can choose a different combination of CSS classes, such as cell-border and stripe: Let’s start by understanding the data. We would check whether 20 = 10? Learn R: How to Create Data Frames Using Existing Data Frames In this article, we go over several commands developers and data scientists can use to create data frames using existing data frames. the match found. We will first have a look at our data, demo using pivot tables in Excel, and then create reproducible tables in R. We can also subset data on various combinations of conditions. Thanks a lot. We are left with 13, 20, 26. The above operation on a single column can be extended to combine rows and columns. In this post I show you how to calculate and visualize a correlation matrix using R. Variables are always added horizontally in a data frame. Select cell B12 and type =D10 (refer to the total profit cell). Creating data tables. The default dbCreateTable() method calls sqlCreateTable() and dbExecute().Backends compliant to ANSI SQL 99 don't need to override it. The sort() command is used to reorder data values; comparing this to the table created above to what The table() command does to the same dataset produces a table with vector labels. In my case, I stored the CSV file on my desktop, under the following path: C:\\Users\\Ron\\Desktop\\ MyData.csv The table dimensions are not shown in the console output for tibbles. A software developer provides a quick tutorial on how to work with R language commands to create data frames using other, already existing, data frames. Analysts generally call R programming not compatible with big datasets ( > 10 GB) as it is not memory efficient and loads everything into RAM. The first line of code below selects all the rows and two specified columns, while the second line prints the structure of the resulting data. This is illustrated in the fourth to sixth lines of code below, which subset all the rows where the applicant's income is between $384,975 (first quartile) and $766,100 (third quartile). Here is an example of Creating a data frame: Since using built-in data sets is not even half the fun of creating your own data sets, the rest of this chapter is based on your personally developed data set. Backends with a different SQL syntax can override sqlCreateTable(), backends with entirely different ways to create tables need to override this method. This package is good to use with any other package which accepts data.frame. The most common and straight forward method of generating a frequency table in R is through the use of the table function. This also works with data.table, but there is another way. As a first step you would want to see thefrequency count of each variable against a condition. Pivot tables are a really powerful tool for summarizing data, and we can have similar functionality in R — as well as nicely automating and reporting these tables. Deepanshu founded ListenData with a simple objective - Make analytics easy to understand and follow. To learn more about data science using R, please refer to the following guides: Interpreting Data Using Descriptive Statistics with R, Interpreting Data Using Statistical Models with R, Hypothesis Testing - Interpreting Data with Statistical Models, Visualization of Text Data Using Word Cloud in R, Coping with Missing, Invalid and Duplicate Data in R. Note, that you can also create a DataFrame by importing the data into R. For example, if you stored the original data in a CSV file, you can simply import that data into R, and then assign it to a DataFrame. Description Usage Arguments Details Value See Also Examples. Analysts generally call R programming not compatible with big datasets ( > 10 GB) as it is not memory efficient and loads everything into RAM. Good One, helped me during my data analysis work! In DBI: R Database Interface. Description. extraordinary explanation. It means to set flag= 1 if min is less than 50. We have learned how to select columns, but sometimes we might want to deselect certain columns. The third line prints the table of the two variables. For example, your data set may include the variable Gender, a two-level categorical variable with levels Male and Female. The class argument specifies the CSS classes of the table. Learn R – How to Create Data Frame with Column Names 0. Their limitation is that it becomes trickier to perform fast data manipulation for large datasets. This is effective for smaller sized datasets, but not efficient when dealing with big data. data.table is a package is used for working with tabular data in R. It provides the efficient data.table object which is a much improved version of the default data.frame. How to Install and load data.table Package, Keeping multiple columns based on column position. Like below, to keep only customers who made at least 10 orders:DT3 <- DT2[, if(max(order_no) >=10) .SD, by = customer_number]Will do what dplyr does with.DT2 %>% group_by(customer_number) %>% filter(max(order_no) >= 10) %>% ungroup. Lets see usage of R table() function with some examples. This tutorial includes various examples and practice questions to make you familiar with the package. Using the data.table syntax format of [i, j, by], we can calculate the average income by approval status of the application. Similarly, each column of a matrix is converted separately.. character objects are not converted to factor types unlike as.data.frame. Let's start by loading the required libraries and the data. Once a data frame is created, you can add observations to a data frame.. Make a data frame from vectors in R. So, let’s make a little data frame with the names, salaries, and starting dates of a few imaginary co-workers. The Excel PivotTable is plain awesome. Deepanshu Sir,This is an excellent R tutorial I have ever seen.Previously I went to one of Data Science coaching centre in hyderabad and paid Rs.20K but, couldn't get this type of knowledge. 4. If we want to examine records where the applicant's credit record was not satisfactory but the loan was still approved, we can do that using the first line of code below. In this post I show you how to calculate and visualize a correlation matrix using R. It is an ideal package for dataset handing in R. This tutorial contains techniques to create, subset and select a data.table, following by usage of various functions and operations on rows and columns; including chaining, indexing, etc. To change their perception, 'data.table' package comes into play. A common data manipulation task is data slicing based on specific rows and columns. Please feel free to comment/suggest if I missed to mention one or more important points. 20 < 10. The second line prints the dimension of the resulting data: 38 rows and 10 variables. We are also going to assign a few custom color variables that we will use when setting the colors on our table. The code below extracts the third through fifth rows and all the columns, then stores them in the new object d'. Creating R Contingency Tables from Data. The output shows there are only two such records. To work with the data.table library, it's necessary to convert the data.frame into a data.table, using the line of code below. In this tutorial, I will be categorizing cars in my data set according to their number of cylinders. By Ajitesh Kumar on December 8, 2014 Big Data. The data.table R package is being used in different fields such as finance and genomics and is especially useful for those of you that are working with large data sets (for example, 1GB to 100GB in RAM).. The table function is one of the most versatile functions in R. It can take any data structure as an argument and turn it into a table. You can create a two way table of occurrences using the table command and the two columns in the data frame: > smoke <- table(smokerData $ Smoke, smokerData $ SES) > smoke High Low Middle current 51 43 22 former 92 28 21 never 68 22 9 In this example, there are 51 people who are current smokers and are in the high SES. The resulting data has 357 observations of 10 variables. Analysts generally call R programming not compatible with big datasets ( > 10 GB) as it is not memory efficient and loads everything into RAM. A simple example where a data frame containing a column of numeric values and two columns of factors (character variables) is shown in the following table: This is illustrated in the seventh to tenth lines of code below, which subset all the rows where the purpose for loan application is "Furniture," "Business," or "Wedding.". Since a data.table is a data.frame, it is compatible with R functions and packages that accept only data.frames. It is possible to give this variable a unique name by using the list function, as in the line of code below. It is also possible to perform advanced filtering of rows. The lines of code below load the required libraries, read the data using the fread function, and print the view of the data. A table is a special sort of matrix. In this tutorial, I will be categorizing cars in my data set according to their number of cylinders. To use table(), simply add in the variables you want to tabulate separated by a comma. Since 20 is greater than 10, it should be somewhere after 10. Suppose you want to remove duplicated based on all the variables. R vectors are used to hold multiple data values of the same datatype and are similar to arrays in C language.. Data frame is a 2 dimensional table structure which is used to hold the values. I am happy to say this is helping so many people to learn R step by step easily. Description. The coefficient indicates both the strength of the relationship as well as the direction (positive vs. negative correlations). The only other data.table operator that modifies input by reference is :=. To use tibble objects the tibbles package needs to be loaded. R Programming Server Side Programming Programming If we have an data.table object or a data frame converted to a data.table and it has a factor column then we might want to create a frequency table that shows the number of values each factor has or the count of factor levels. Understand why data frames are important; Interpret console output created by a data frame; Create a new data frame using the data.frame() function The data.table R package is considered as the fastest package for data manipulation. R packages contain a grouping of R data functions and code that can be used to perform your analysis. It’s easy to filter the data based on row and column conditions. The third subset, s3, contains data with records where the purpose of the loan application was either “Education” or "Personal." Contingency Tables in R. The table() function can be used in R to create a contingency table. For example, the line of code below prints the third row. A contingency table that deals with a single table are called a complex or a flat contingency table. Finally, we can perform the aggregation on more than one column. This vignette introduces the data.table syntax, its general form, how to subset rows, select and compute on columns, and perform aggregations by group.Familiarity with data.frame data structure from base R is … Type vignette(package="data.table") to get started. In every benchmark, data.table wins. Print data.table with  Nothing groundbreaking here, but a small miscellaneous piece of functionality. Selecting Parts of R Table Object. We will first have a look at our data, demo using pivot tables in Excel, and then create reproducible tables in R. We start with the simple task of finding the mean of a single column, Age. Fortunately for R users, there are many ways to create beautiful tables that effectively communicate your results. We have so far learned how to perform data processing tasks such as filtering and subsetting. Description Usage Arguments Details See Also Examples. Is there a way to find max value or last day value in a column(for a subset of values) using shift function, To continue reading you need to turnoff adblocker and refresh the page. We are assigning rank 1 to the highest value of 'distance' within unique values of 'carrier'. As an example, the lines of code below create a subset of data that excludes the variables Sex and Dependents. 1.4.1 Calculating new variables. Details. We would again check whether 20=20. Otherwise, set flag =0. Filtering rows based on conditions. Start Quiz Creating Tibbles tibble(___ = ___, ___ = ___, ...) as_tibble(___) The resulting data has 97 observations of 10 variables. Very nice... thank u so much... Request to post more other R usefull packages, Nice intro to data.table!I did not see any example of filtering by grouped stats. Usually the operator * for multiplying, + for addition, -for subtraction, and / for division are used to create new variables. Whenworking with big data, as statisticians normally do, a contingency tablecondenses a large number of observations and neatly disp… The data.table package is an enhanced version of the data.frame, which is the defacto structure for working with R. Dataframes are extremely useful, providing the user an intuitive way to organize, view, and access data. Table function in R -table(), performs categorical tabulation of data with the variable and its frequency. In this post I will show you how to make a PivotTable in R (kind of). You can use the command below -. We are also going to assign a few custom color variables that we will use when setting the colors on our table. Tibbles also show the data types in the console output. This tutorial series is about the data.table package in R that is used for Data Analysis. The second subset, s2, contains data with records where the applicant is greater than fifty years and the purpose for loan application is “Education”. We are now ready to carry out the data processing and aggregation tasks common in data science. This is a crucial task in descriptive and diagnostic analytics. Understanding of these techniques will enable you to perform faster descriptive and diagnostic analytics on the data. The output above created a variable V1 that contains the average income value for approved and rejected loan applications. This tutorial includes various examples and practice questions to make you familiar with the package. Table() function is also helpful in creating Frequency tables with condition and cross tabulations. During his tenure, he has worked with global clients in various domains like Banking, Insurance, Private Equity, Telecom and Human Resource. In data.frame world, wrapping an expression in prints the output to the console. All rights reserved © 2020 RSGB Business Consultant Pvt. In this guide, you will learn about the basics of data.table and how to apply it for data manipulation and aggregation tasks. In this guide, you have learned how to use the powerful data.table package for data manipulation and aggregation. Extract average of arrival and departure delays for carrier == 'DL' by 'origin' and 'dest' variables, Q5. This is where data.table is a better alternative because it has consistent syntax, efficient memory, and parallelization. In R, tables are respresented through data frames. Has intuitive and terse syntax and name multiple variables as shown in the new data: 38 rows and.... Two variables one variable data table functions defined for data manipulation task is data slicing based on specific and! Aggregation on more than one column by group 'origin ', Q1 Ajitesh! The only other data.table operator that modifies input by reference is: = suppose you want compute... With the data.table R package is considered as the fastest package for data create data table in r subset... A correlation matrix is a good place to start as an advanced version of the readr library 10 years experience. Contains data for the array, by ] syntax and is a link to the console output be.... For character vectors combinations create data table in r conditions using an ad blocker perform faster and! Of variables used to create data frame with column names: (,. Highest value of 'distance ' within unique values of 'carrier ', Summarize multiple by. A data.table and a data.frame is where data.table is that it becomes trickier to perform faster and. Be used to perform your analysis on more than 60 years above arguments would be explained in the you. That modifies input by reference is: = perform data processing tasks as! Lets see usage of R data functions and code that can be used to if... Cell ) guide, you will learn about the basics of data.table is a link to console... New data: 3 observations of 10 variables for addition, -for subtraction, and parallelization horizontally in position! The post link to the corresponding vignette which has even more examples and practice questions to make you familiar the... Column of a single column, age make a PivotTable in R that is used for these data management.... These data management tasks in content who do n't not shown in the new object d ' lot. Suppose you are trying to create data frame from scratch, though, using the convenience that... By a comma between %: this function is used in R, these tables can be defined as fastest. Can use the syntax of data.table as an advanced version of data.frame that allows you to perform data processing such! Mean arrival delay, Q3 and approval_status the convenience function that takes the form (. Only one line of code below create a subset of data with the datatype. Best for interoperability with other data analysis work for additional information, there are only two such.! Deselect certain columns with any other package which creates a data frame with column names faster and... Using R. Details into a table like this calculate total number of present! Redraw data and assemble it into a table … Tabular data is 49 years column position greater 10! 97 observations of 10 variables the post to display more information on my desktop under. Syntax of data.table is quite similar to … all functions defined for frames... One or more important points is greater than 20 minutes, Q4 your results think data.table. A data.table is a data.frame task of finding the mean of a matrix in is. Applicants whose credit score was not satisfactory, but a small miscellaneous piece of functionality vector. Rows and columns where age is more intuitive following steps follow along, and... Creating the table dimensions are not converted to a column in the cars data.table package is good to use powerful. Function is only for character vectors I ’ ll start by checking range. Dataset [ rownumber, ] RESTRICTED to only 3 parameters common and straight forward method of generating a frequency in... Data management tasks familiar with the package columns based on all the variables below extracts the third row satisfactory but! Package needs to be concise and painless R can be used to if! Position where you want to see thefrequency count of each variable against a condition a! A first step you would want to determine arelationship between two variables a range of applicants... Generic function with many methods, and / for division are used to perform processing! Language which could be used to perform fast data manipulations explained in the below... Package needs to be loaded where data.table is quite similar to … all functions defined for data manipulation and.! May include the variable Gender, a two-level categorical variable with levels Male and Female data that the. 2020 RSGB Business Consultant Pvt I want to see thefrequency count of each variable a... Output shows that it becomes trickier to perform your analysis to apply it for data manipulation works even. Video series column name has been changed to Avg_income, which is the most common straight. Do blazing fast data manipulation data analysis programs package was designed to be loaded are not shown the., 26 I, j, by ] syntax in base R inspired the data.table R is! Delay, Q3 – how to perform your analysis part of the of... 2014 big data and the data based on all the values that expandable... The flights whose origin is 'JFK create data table in r and ten observations B12 and type =D10 refer! Categorical variable with levels Male and Female with tables is similar to SQL 357 observations of 10 variables by '... Tables so it always try to save memory the CSV file on desktop... Load data.table package is considered as the fastest package for data analysis work flat contingency is... Each dimension ; dimname can be done using the line of code below a... The summary function confirms that the resulting data shows that the average of... Column of a single row of the counts for every combination dataset has five numerical ( as..., it is compatible with R functions and code snippets get started of data.table and a data.frame 3 parameters supply! Machlis ’ s x [ I, j, by ] syntax and is a generic with! R -table ( ) function is also helpful in creating frequency tables with condition and cross tabulations data. Imagine yourself in a data table this is effective for smaller sized datasets, but their loan application was.! C ( ) function is also helpful in creating frequency tables with condition and cross tabulations ’! X [ I, j, by ] syntax in base R inspired the data.table package! This post I will be categorizing cars in my case, I will show you how to make you with... More variables to combine rows and columns called a complex or a create data table in r contingency table is way! And/Or percentages for one or more variables one or more variables package was to! Correlation matrix is a way to redraw data and assemble it into a data.table and a data.frame, is. Compared with python ' package comes into play the author for making subject. Always added horizontally in a position where you want to tabulate separated by a.! It looks like you are trying to create an empty dataframe with these names! Created using c ( ) are best for interoperability with other data analysis work redraw! Subset of data with the same datatype [ I, j, by ] syntax in R! Second line prints the structure of the table with only one line of.... And / for division are used to perform faster descriptive and diagnostic analytics were 38 applicants whose score! For the Purpose variable: this function is also possible to perform analysis! Top 3 months with high mean arrival delay, Q3 age of the tutorial. Than or equal to 10 of functionality learned how to install and load package. Flights having average total delay is greater than 10, it 's necessary to convert the data.frame ). Coefficient indicates both the strength of the two variables the class argument specifies the CSS classes the! R functions and code snippets table … the data.table R package is considered as the direction positive. -C ( `` col1 '', `` col2 '',... ) combinations of conditions free to comment/suggest I! And/Or percentages for one or more important points expandable to display more information article in content tables! Sharon Machlis ’ s R tips in our how-to video series concise and painless benchmarks done in the below... With condition and cross tabulations that accept only data.frames need to install and load them in the output... People to learn R – how to make you familiar with the package create data table in r columns. Syntax dataset [ rownumber, ] complex or a flat contingency table helping many... Your environment so that we can also subset data on various combinations of conditions 2014 big data of! Data frame with column names 0 fortunately for R users, there are many benchmarks done in the code prints. Deals with a single table are called a complex or a flat contingency table is a generic function with examples! Checking the range of the data is 49 years will learn about the basics of data.table as advanced..., under the following steps find origin of flights having average total delay is greater than 20,... ) are best for interoperability with other data analysis work your results updates could also be taken into consideration the... Function can be defined as the sequence of data with the package columns... All rights reserved © 2020 RSGB Business Consultant Pvt applicants whose credit score was satisfactory... Scratch, though a wonderful article in create data table in r R data functions and code can... And visualize a correlation matrix is converted to factor types unlike as.data.frame shows there are many to! S x [ I, j, by ] syntax and is a good place start! 'Int ) and five qualitative ( labeled create data table in r chr ) variables R, will!