r - Unlist list of lists that have matrix elements to a list of matrices -

suppose a, b , c matrices. , have list of them this:

  list(a,list(b,c)) 

i want convert this:

  list(a,b,c) 

the unlist function convert matrices vectors!

for example:

a=matrix(1:10,nrow=2) b=list(a,list(a,a)) unlist(b) 

here recursive implementation:

flatten2 <- function(x) if(is.list(x)) reduce(c, lapply(x, flatten2)) else list(x) 

then:

str(flatten2(b))   # list of 3 matrices: # list of 3 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 

and more complex:

c <- list(a, list(list(a, a), a)) str(flatten2(c)) # list of 4 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 #  $ : int [1:2, 1:5] 1 2 3 4 5 6 7 8 9 10 

also, "wordier" faster version (this 1 tested pierre):

flatten <- function(x) {   res <- list()   for(i in x) res <- c(res, if(is.list(i)) recall(i) else list(i))   res } 

you make flatten2 little faster replacing reduce do.call, little less cute. flatten remains fastest change.