Question

I have a list of different data types (factors, data.frames, and vectors, all the same length or number of rows), What I would like to do is subset each element of the list by a vector (let’s call it rows) that represents row names.

If it was a data.frame() I would:

x <- x[rows,] 

If it was a vector() or factor() I would:

x <- x[rows]

So, I’ve been playing around with this:

x <- lapply(my_list, function(x) ifelse(is.data.frame(x), x[rows,], x[rows]))

So, how do I accomplish my goal of getting a list of subsetted data?

Answer 1

I think this is YAIEP (Yet Another If Else Problem). From ?ifelse:

ifelse returns a value with the same shape as test which is filled
with elements selected from either yes or no depending on whether the
element of test is TRUE or FALSE.

See the trouble? Same shape as test.

So just do this:

l <- list(a = data.frame(x=1:10,y=1:10),b = 1:10, c = factor(letters[1:20]))

rows <- 1:3

fun <- function(x){
    if (is.data.frame(x)){
        x[rows,]
    }
    else{
        x[rows]
    }
}

lapply(l,fun)