R - unlist into dataframe

Question

I have a list of vectors in R:

[[1]]
[1] 1 2 3 4

[[2]]
[1] 7 9 1 4

[[3]]
[1] 8 2 1

[[4]]
[1] 8 9 0 7

And I want to make a dataframe out of them. The problem is, I can't simply use unlist and then reorganize, because not all the vectors are the same length – I want NAs in my dataframe when that happens. The final result should look like this:

Col1  Col2  Col3  Col4
1     2     3     4
7     9     1     4
8     2     1     NA
8     9     0     7

Is there a way to do this?

Answer 1

Using purrr you can do the following:

require(purrr)
L <- list(1:4, c(7,9,1,4), c(8,2,1), c(8,9,0,7))
map_df(L, ~as.data.frame(t(.)))

Which gives you:

  V1 V2 V3 V4
1  1  2  3  4
2  7  9  1  4
3  8  2  1 NA
4  8  9  0  7

Base R approach:

clen <- vapply(L, length, integer(1))
mat <- matrix(NA, nrow = length(L), ncol = max(clen))
for(i in seq_along(L)){
  mat[i, seq(1, clen[i])] <- L[[i]]
}
as.data.frame(mat)

Answer 2

Try this in base R (where ls is your list object):

data.frame(t(sapply(ls, function(x) x[1:max(lengths(ls))])))

Which given your data will give you:

#  X1 X2 X3 X4
#1  1  2  3  4
#2  7  9  1  4
#3  8  2  1 NA
#4  8  9  0  7

In general, c(1:5)[1:7] will give you

#[1]  1  2  3  4  5 NA NA