multicore::sapply?

Question

Is there anything like sapply in the multicore library? Or do I have to unlist(mclapply(..)) in order to achieve this?

If it does not exist: what would the reasoning be?

Thanks in advance and sorry if this is a stupid question!

Answer 1

In the library parallel, you have mcmapply which, like mapply in base, takes a SIMPLIFY argument. It is TRUE by default. Here is an example use:

library(parallel)
mcmapply(sqrt,split(1:8,1:8))
#        1        2        3        4        5        6        7        8
# 1.000000 1.414214 1.732051 2.000000 2.236068 2.449490 2.645751 2.828427

Compare this to the use of mclapply.

mclapply(split(1:8,1:8),sqrt)
# $`1`
# [1] 1
# 
# $`2`
# [1] 1.414214
# ...

Answer 2

If you look at the code of sapply (and its helper function simplify2array) you will see that unlist(obj) is exactly what will be done in the case where obj is a list of items all of length==1. sapply is a lot more complex than just unlisting lists, however. What is still very unclear is what problem you are trying to solve.