I have an asymmetric list, i.e., the number of elements in each sub-list differ. How can I convert the list to a matrix?
Below I begin with a symmetric list and convert it to a matrix two different ways.
# create a symmetric list
my.list1 <- list(c(1,2,3,4),c(5,6,7,8),c(9,10,11,12))
my.list1
# convert symmetric list to a matrix
mat.a1 <- matrix( unlist(my.list1), nrow=length(my.list1), byrow=T )
mat.a1
# alternative method to convert symmetric list to a matrix
mat.b1 <- do.call(rbind, my.list1)
mat.b1
Next I create an asymmetric list:
# create an asymmetric list
my.list2 <- list(c(1,2,3,4),c(5,6,7,8,9),c(10,11,12,13))
my.list2
Here is the desired matrix:
# desired result
# [,1] [,2] [,3] [,4] [,5]
# [1,] 1 2 3 4 NA
# [2,] 5 6 7 8 9
# [3,] 10 11 12 13 NA
First, extend each vector in your list with NAs to get vectors of the same length. Then create your matrix. For example:
max.len <- max(sapply(my.list2, length))
corrected.list <- lapply(my.list2, function(x) {c(x, rep(NA, max.len - length(x)))})
mat <- do.call(rbind, corrected.list)
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