One common procedure you may want to perform in R is using a for loop to repeat some process several times, then appending the results of the process to a vector. This tutorial explains how to do so using two different examples.

**For Loop Example – Numeric Vector**

The following example shows how to create a loop that picks a random number between 1 and 10, 20 times, then appends each number to a numeric vector.

#create an empty numeric vector num_vector <- numeric() #create a loop that picks a random number between 1 and 10, 20 times. #Append each result to the numeric vector defined above. for(i in 1:20) { #generate random number between 1 and 10 number <- runif(1, 1, 10) #append this random number to the i-th position in the vector num_vector[i] <- number } #view vector of 20 random numbers num_vector # [1] 6.537753 3.008067 4.979126 4.444119 3.786783 7.159006 2.369399 5.344314 # [9] 1.161575 6.197420 9.658708 3.666595 1.691599 3.053068 9.825492 5.015388 #[17] 5.534652 5.362132 9.935340 1.593897

**For Loop Example – Character Vector**

The following example shows how to create a loop that picks a random character from the alphabet 20 times, then appends each number to a character vector.

#create an empty character vector char_vector <- character() #create a loop that picks a random character from the alphabet 20 times. #Append each character to the character vector defined above. for(i in 1:20) { #select random character charac <- sample(letters, 1) #append this random character to the i-th position in the vector char_vector[i] <- charac } #view vector of 20 random characters char_vector # [1] "o" "f" "z" "x" "f" "k" "f" "i" "z" "i" "e" "a" "m" "j" "x" "x" "y" "q" "z" #[20] "g"