Vectorized operations tend to work so that a logic is applied to EVERY element of a vector.
However, let's assume I have a vector i.e.
> 1:10
[1] 1 2 3 4 5 6 7 8 9 10
I would like to apply a function, say, multiplication by 0.5 to every element except the first and the last element: I would like to multiply them by 0.3.
Is there a dplyr (or any other vectorized) way to do this?
I know that sapply with if-else structure would do the trick i.e.
sapply(seq(1:10), #I know seq() is not actually needed in this particular case
function(i) {
if(i == 1 | i == length(1:10)) {
(1:10)[i]*0.3
} else {
(1:10)[i]*0.5
}
}
)
...but vectorized solution with an index dependent case_when would be nice.
Since you explicitly mentioned case_when in your title, one index dependent case_when solution could be:
library(dplyr)
x <- 1:10
data.frame(x) %>%
mutate(x_mult = case_when(
row_number() == 1 | row_number() == n() ~ x * 3,
TRUE ~ x * 5
))
Output:
x x_mult
1 1 3
2 2 10
3 3 15
4 4 20
5 5 25
6 6 30
7 7 35
8 8 40
9 9 45
10 10 30