6 Loops

If you want to repeat a process many times you will need to create a loop:

6.1 Basic for Loop structure

for (x in 1:4) {
 print(x)  
}

6.2 Looping through a vector

loopvector <- c("a","b","c")

for (x in 1:length(loopvector)) {
 print(loopvector[x])  
}

## [1] "a"
## [1] "b"
## [1] "c"

6.3 Creating a List in a Loop

newList <- list()  # An empty List

for (x in 1:5) {
 newList[[x]] = x^2  # Inserts an element into the List  
}

newList[[3]] 

## [1] 9

6.4 Looping with apply functions

An alternative to using ‘for’ loops is to use the apply functions. This means turning process into a function and then applying the function to a vector/matrix/list:

loopvector <- c("a","b","c")

print_list <- function(x) {
  print(x)
}

test <- sapply(loopvector, print_list)

## [1] "a"
## [1] "b"
## [1] "c"

There are various types of apply function.
sapply will usually return output as a vector.
lapply will usually return output in a list.