Replications (Repetitions)
Following the previous exercise, the simplest case of replication is when we want to repeat one value a number of times.
# the thing you want to repeat
x <- "Slartibartfast"
# the number of times you repeat it
times <- 4
# the starting values
count <- 1
result <- NULL
# repeat as long as needed
while(count <= times){
# the final result
result <- c(result, x)
# increment counter
count <- count + 1
}
result
[1] "Slartibartfast" "Slartibartfast" "Slartibartfast" "Slartibartfast"
The rep() function
Replications are extremely common in R, and for this reason, there is a convenience function: rep(). Check out its help file with ?rep!
In its basic form, rep() function takes at least two arguments: the thing you want to replicate (x - can be of any type!), and how many times you want to repeat it (times).
For instance, if you want to repeat the example above you only have to say, which is considerably shorter.
rep("Slartibartfast",4)
[1] "Slartibartfast" "Slartibartfast" "Slartibartfast" "Slartibartfast"
Repeating multiple values
Note that since the combine function (c()) can be used with multiple values, you can actually repeat entire vectors with the examples above (also with the while loop)!
a <- c(1,100,1000)
rep(x=a, 3)
[1] 1 100 1000 1 100 1000 1 100 1000
repeating the vector a 3 times.
More complex repetitions (later)
There are more complex ways to replicate a particular entity: these give you some of the examples, which we will see at a later point.
rep(a, each=3)rep(a, c(3,2,1))rep(a, length.out=10)