R list get first item of each element

Question

This should probably be very easy for someone to answer but I have had no success on finding the answer anywhere.

I am trying to return, from a list in R, the first

Answer 1

You can do

 output <- sapply(d, function(x) x[1])

If you don't need the names

 names(output) <- NULL

Answer 2

sapply(d, "[[", 1) should do the trick.

A bit of explanation:

sapply: iterates over the elements in the list
[[: is the subset function. So we are asking sapply to use the subset function on each list element.
1 : is an argument passed to "[["

It turns out that "[" or "[[" can be called in a traditional manner which may help to illustrate the point:

x <- 10:1
"["(x, 3)
 # [1] 8