How to properly avoid if-expressions by using vector indices? - r

Question

x is a vector of integers ranging between 1 and 100
I created a function that determines in which category a number is:
x∈[1,20]: small
x∈[21,50]: med
x∈[51, 100]:large
Here the function:
x <- c(1:99)
vector.fun<-function(x){
x[x >= 1 & x <=20] <-"small"
x[x >= 21 & x <=50] <-"med"
x[x >=51 & x <=99] <-"large"
return(x)
}
vector.fun(89)
However as you can see, in the function my vector is 1:99 instead of 1:100, for some reason when i change it to:
x <- c(1:100)
vector.fun<-function(x){
x[x >= 1 & x <=20] <-"small"
x[x >= 21 & x <=50] <-"med"
x[x >=51 & x <=100] <-"large"
return(x)
}
vector.fun(100)
it doesn't recognise any number from the last line: x[x >=51 & x <=100] <-"large" and when it does it returns "med" instead of "large" as it should be.
what am I doing wrong? Which changes should I do in my function in order that 100 is included in the parameter and returns "large"?

Answer 1

It is indeed a coercion problem as mentioned in the comments above.
If you want to keep your function structure the way you created it, you can alter it as follows:
vector.fun<-function(y){
x <- y
x[y >= 1 & y <=20] <-"small"
x[y >= 21 & y <=50] <-"med"
x[y >=51 & y <=100] <-"large"
return(x)
}
Although the solution suggested by #alexis_laz is more concise and elegant:
vector.fun<-function(x){
cut(x, c(0,20,50,100), labels = c("small", "med", "large"))
}
Keep in mind, this second version will produce a factor type vector, while the first version will produce a character type vector.