Exercise 2: R vector operations
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Find a function FUN that leads to the following output:
x <- sample(1:10) FUN(x) - FUN(-x) ## [1] 11 11 11 11 11 11 11 11 11 11
Hint: aim to keep the answer simple. The main logic of the function can often be summarized in a single line of R code.
Answer 1: click to reveal
We can write the function as follows:
FUN <- function(x) {
return(sort(x))
}
Based on this definition of FUN we get:
FUN(x) ## [1] 1 2 3 4 5 6 7 8 9 10 FUN(-x) ## [1] -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
which fulfills the puzzle condition:
FUN(x) - FUN(-x) ## [1] 11 11 11 11 11 11 11 11 11 11
Answer 2: click to reveal
Another possible definition of FUN that builds on Puzzle 1 is:
FUN <- function(x) {
return(rep(max(x), times = length(x)))
}
Based on this definition of FUN we get:
FUN(x) ## [1] 10 10 10 10 10 10 10 10 10 10 FUN(-x) ## [1] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
which fulfills the puzzle condition:
FUN(x) - FUN(-x) ## [1] 11 11 11 11 11 11 11 11 11 11
As we have seen in exercise 1 the max can also be replaced with min and the result still holds:
FUN <- function(x) {
return(rep(min(x), times = length(x)))
}
FUN(x) - FUN(-x)
## [1] 11 11 11 11 11 11 11 11 11 11
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