I'm looking for a efficient way for the following transformation:
Example input:
ob <- list(a = 2, b = 3)
Expected output:
key value
1 a 2
2 b 3
Current (verbose) solution:
data.frame(key = names(ob), value = unlist(ob, use.names = FALSE))
Try stack
stack(ob)
# values ind
#1 2 a
#2 3 b
You would need to change the names though. Use setNames
setNames(stack(ob), nm = c("value", "key"))
benchmark
Addressing @Roland's comment, stack seems to be more efficient indeed.stack but OP's solution for efficiency reasons.
n <- 1e5
lst <- as.list(seq_len(n))
names(lst) <- paste0("a", seq_len(n))
library(microbenchmark)
benchmark <- microbenchmark(
snoram = snoram(lst),
markus = markus(lst), times = 50
)
benchmark
#Unit: milliseconds
# expr min lq mean median uq max neval
# snoram 2.475258 2.594479 2.739639 2.652843 2.715575 5.92216 50
# markus 114.387692 119.028200 134.745626 137.524606 144.045112 162.11510 50
Functions used (so far)
snoram <- function(l) {
data.frame(key = names(l), value = unlist(l, use.names = FALSE),
stringsAsFactors = FALSE) # this gives a hugh performance gain
# thanks to @Roland
}
markus <- function(l) {
setNames(stack(l), nm = c("value", "key"))
}