How to split list at every 10th item in R? - r

Question

I have a list of 100 items.
I want to split it after each 10th item in Code 1.
Code 2 is about a list of two former lists and splitting it to 20 lists of 10 items each.
Code 1
Expected output: ten lists of 10 items.
A <- 100
a <- rnorm(A) # [1:100]
n <- 10
str(a)
# Not resulting in equal size of chunks with vectors so reject
# http://stackoverflow.com/a/3321659/54964
#d <- split(d, ceiling(seq_along(d)/(length(d)/n)))
# Works for vectors but not with lists
# http://stackoverflow.com/a/16275428/54964
#d <- function(d,n) split(d, cut(seq_along(d), n, labels = FALSE))
str(d)
Test code 2
Input: a list of two lists
aa <- list(a, rnorm(a))
Expected output: 20 lists of 10 item size
Testing Loki's answer
segmentLists <- function(A, segmentSize) {
res <- lapply(A, function(x) split(unlist(x), cut(seq_along(unlist(x)), segmentSize, labels = F)))
#print(res)
res <- unlist(res, recursive = F)
}
segmentLists(aa, 10)
Output: loop going on, never stopping
OS: Debian 8.5
R: 3.3.1

Answer 1

you can use lapply.
aa <- list(a, rnorm(a))
aa
n <- 10
x <- lapply(aa, function(x) split(unlist(x), cut(seq_along(unlist(x)), n, labels = F)))
y <- unlist(x, recursive = F)
str(y)
# List of 20
# $ 1 : num [1:10] 1.0895 -0.0477 0.225 -0.6308 -0.1558 ...
# $ 2 : num [1:10] -0.469 -0.381 0.709 -0.798 1.183 ...
# $ 3 : num [1:10] 0.757 -1.128 -1.394 -0.712 0.494 ...
# $ 4 : num [1:10] 1.135 0.324 0.75 -0.83 0.794 ...
# $ 5 : num [1:10] -0.786 -0.068 -0.179 0.354 -0.597 ...
# $ 6 : num [1:10] -0.115 0.164 -0.365 -1.827 -2.036 ...
...
length(y)
# [1] 20
to remove the names of the list elements in y ($ 1, $ 2 etc.) you can use unname()
str(unname(y))
# List of 20
# $ : num [1:10] 1.0895 -0.0477 0.225 -0.6308 -0.1558 ...
# $ : num [1:10] -0.469 -0.381 0.709 -0.798 1.183 ...
# $ : num [1:10] 0.757 -1.128 -1.394 -0.712 0.494 ...
# $ : num [1:10] 1.135 0.324 0.75 -0.83 0.794 ...
# $ : num [1:10] -0.786 -0.068 -0.179 0.354 -0.597 ...
...
Using a function, you have to return res at the end of the function.
segmentLists <- function(A, segmentSize)
{
res <- lapply(A, function(x) split(unlist(x), cut(seq_along(unlist(x)), segmentSize, labels = F)))
#print(res)
res <- unlist(res, recursive = F)
res <- unname(res)
res
}