for-Loop Index in R (2 Examples)

In this R tutorial you’ll learn how to use for-loop indices.

Table of contents:

Let’s start right away:

Example Vector

First, we have to create some data through which we can loop in the examples later on:

my_vec <- letters[1:5]                   # Create example vector
my_vec                                   # Print example vector
# [1] "a" "b" "c" "d" "e"

As you can see, we have created a vector object containing five character elements.

Example 1: Print for-Loop Index to Console

This Example explains how to return the current for-loop index to the RStudio console using the print function in R.

For this task, we first have to initialize an index counter:

loop_index_1 <- 0                        # Create index count

Next, we can run a for-loop using our example data and the index counter as shown below:

for(i in my_vec) {                       # Run for-loop
  loop_index_1 <- loop_index_1 + 1
  print(loop_index_1)                    # Print index
}
# [1] 1
# [1] 2
# [1] 3
# [1] 4
# [1] 5

As you can see based on the previous RStudio console output, we used the print function to identify the index of each for-loop iteration.

Example 2: Using for-Loop Index to Name Variables

The indices of for-loops can also be used to create or name variables dynamically. In the following R code, we use the assign and paste0 functions to create new data objects.

As in Example 1, we first have to create an index count:

loop_index_2 <- 0                        # Create index count

Next, we can create variables dynamically using this index count within a for-loop:

for(i in my_vec) {                       # Run for-loop
  loop_index_2 <- loop_index_2 + 1
  assign(paste0("variable_",             # Create variables
                loop_index_2),
         loop_index_2^2)
}

Let’s print our new variables to the RStudio console:

variable_1                               # Return new variables
# 1
variable_2
# 4
variable_3
# 9
variable_4
# 16
variable_5
# 25

Video & Further Resources

Have a look at the following video of my YouTube channel. I show the contents of this article in the video.

The YouTube video will be added soon.

Furthermore, you might read the related tutorials of statisticsglobe.com. I have released several posts already:

• print & cat Functions in R
• paste & paste0 R Functions
• for-Loop in R
• Loops in R
• The R Programming Language

Summary: In this R programming tutorial you learned how to identify and use a for-loop index. In case you have any further questions, please let me know in the comments below.