Convert Mixed-Length named List to data.frame

Question

I have a list of the following format:

[[1]]
[[1]]$a
[1] 1

[[1]]$b
[1] 3

[[1]]$c
[1] 5

[[2]]       
[[2]]$c
[1] 2

[[2]]$a
[1] 3

There i

Answer 1

Here's my initial thought. It doesn't speed up your approach, but it does simplify the code considerably:

# makeDF <- function(List, Names) {
#     m <- t(sapply(List, function(X) unlist(X)[Names], 
#     as.data.frame(m)
# }    

## vapply() is a bit faster than sapply()
makeDF <- function(List, Names) {
    m <- t(vapply(List, 
                  FUN = function(X) unlist(X)[Names], 
                  FUN.VALUE = numeric(length(Names))))
    as.data.frame(m)
}

## Test timing with a 50k-item list
ll <- createList(50000)
nms <- c("a", "b", "c")

system.time(makeDF(ll, nms))
# user  system elapsed 
# 0.47    0.00    0.47