R split out list based on name

Question

Suppose I create the following structure

blah <- c()
for (i in 1:10) {
  blah <- c(blah,list(a=i,b=i+10))
}

I want blah$a to be a vector of (1,2,3,4,5,6,7,8,9,10) and blah$b to be a vector of (11,12,13,14,15,16,17,18,19,20).

For the life of me, I can't figure out how to do this.

Answer 1

I think this should work. I first split your list according to the names of elements and then "unlist" the list of list inside each list element. You can also unname each vector (not shown). See code:

lapply(split(x = blah, f = names(blah)), unlist)

$a
 a  a  a  a  a  a  a  a  a  a 
 1  2  3  4  5  6  7  8  9 10 

$b
 b  b  b  b  b  b  b  b  b  b 
11 12 13 14 15 16 17 18 19 20 

In comments, @David mentions

split(unlist(blah), names(blah))

which also works and is probably more efficient.

Answer 2

Actually you can avoid loops:

blah <- list(a = 1:10, b = 1:10+10)

And you get this:

# > blah
# $a
# [1]  1  2  3  4  5  6  7  8  9 10
# 
# $b
# [1] 11 12 13 14 15 16 17 18 19 20

# > blah$a
# [1]  1  2  3  4  5  6  7  8  9 10

with loop:

for (i in 1:10) {
  blah$a[i] <- i
  blah$b[i] <- i+10
}