Apply Function to data.table in Each Specified Column in R (Example)


This page shows how to use the same function for a predefined set of variables in the R programming language.

Table of contents:

Let’s take a look at some R codes in action…


Example Data & Packages

For this tutorial, we first need to install and load the data.table package:

install.packages("data.table")                                  # Install data.table package
library("data.table")                                           # Load data.table

Now, we can create a data.table in R as follows:

data <- data.table(x1 = 1:5,                                    # Create data.table
                   x2 = letters[1:5],
                   x3 = 3)
data                                                            # Print example data
#    x1 x2 x3
# 1:  1  a  3
# 2:  2  b  3
# 3:  3  c  3
# 4:  4  d  3
# 5:  5  e  3

Have a look at the previous output of the RStudio console. It shows that our data.table consists of five rows and three columns.


Example: Apply Function to Each Specified data.table Column Using lapply, .SD & .SDcols

In this Section, I’ll explain how to call a function for certain variables of a data.table using a combination of the lapply, .SD, and .SDcols functions. Consider the following list of variable names:

mod_cols <- c("x1", "x3")                                       # Columns that should be modified

Now, we can apply the following line of R code to compute the power of 2 for each cell of the specified columns:

data[ , (mod_cols) := lapply(.SD, "^", 2), .SDcols = mod_cols]  # Modify data
data                                                            # Print updated data
#    x1 x2 x3
# 1:  1  a  9
# 2:  4  b  9
# 3:  9  c  9
# 4: 16  d  9
# 5: 25  e  9

As you can see based on the previous RStudio console output, our data was updated.


Video, Further Resources & Summary

Do you want to learn more about the application of functions to columns? Then you might watch the following video of my YouTube channel. In the video, I show the R programming codes of this tutorial.


The YouTube video will be added soon.


Besides the video, you may read the other R tutorials of my website.


This tutorial illustrated how to call the same function for a list of variables of a data.table in the R programming language. Tell me about it in the comments, if you have any additional questions.


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