Select Data Frame Column Using Character Vector in R (Example)
In this R programming tutorial you’ll learn how to extract a data frame variable based on a character string.
Table of contents:
- Creating Example Data
- Example: Select Column with [] Instead of $-Operator
- Video, Further Resources & Summary
Let’s just jump right in…
Creating Example Data
First, let’s create some example data:
data <- data.frame(x1 = 1:5, # Creating example data x2 = letters[1:5], x3 = 7) data # Printing example data # x1 x2 x3 # 1 1 a 7 # 2 2 b 7 # 3 3 c 7 # 4 4 d 7 # 5 5 e 7
Our data frame contains five rows and three variables.
Let’s also use the colnames function to create a data object containing the column names of our data frame:
data_cols <- colnames(data) # Storing column names data_cols # Printing column names # "x1" "x2" "x3"
Example: Select Column with [] Instead of $-Operator
Typically, we would use the $-operator to select certain variables from our data frame. However, if we want to extract variables dynamically based on a character string this is not possible. Let’s give it a try:
data$data_cols[1] # Trying to use $-operator # NULL
As you can see, the previous R code is returning NULL.
Fortunately, we can use square brackets instead. Have a look at the following R code:
data[ , data_cols[1]] # Subset using square brackets # 1 2 3 4 5
As you can see, the previous syntax returned the values of our first variable x1 (i.e. the first element in data_cols). For instance, subsetting variables with square brackets instead of the $-operator can be very useful in for-loops, while-loops, or user-defined functions.
Video, Further Resources & Summary
Do you need further info on the R codes of this tutorial? Then you may watch the following video of my YouTube channel. In the video, I’m explaining the topics of this tutorial in a live session.
Please accept YouTube cookies to play this video. By accepting you will be accessing content from YouTube, a service provided by an external third party.
If you accept this notice, your choice will be saved and the page will refresh.
Additionally, you might want to read the other articles of my website. I have released several posts about the extraction of variables from data frames already.
- Extract Certain Columns of Data Frame
- Drop Data Frame Columns by Name
- Extract Column of dplyr Tibble
- The R Programming Language
Summary: In this tutorial you learned how to access the elements of a variable using a character string in R programming. Let me know in the comments section, in case you have further questions.
Statistics Globe Newsletter