Search code examples
rlistmatrixcoercion

Convert a vector of lists with uneven length to a matrix

I have a vector, well a data frame with only one column, that contains lists of uneven lengths:

data = list(
c(349, 364, 393, 356, 357, 394, 334, 394, 343, 365, 349),
c(390, 336, 752, 377),
c(670, 757, 405, 343, 1109, 350, 372),
c(0, 0),
c(),
c(1115, 394, 327, 356, 408, 329, 385, 357, 357))

and I would like to convert it to a matrix, filling the gaps with NA. So it should look something like this:

349, 364, 393, 356, 357, 394, 334, 394, 343, 365, 349
390, 336, 752, 377, NA,  NA,  NA,  NA,  NA,  NA,  NA
670, 757, 405, 343, 1109,350, 372, NA,  NA,  NA,  NA
0,   0,   NA,  NA,  NA,  NA,  NA,  NA,  NA,  NA,  NA
NA,  NA,  NA,  NA,  NA,  NA,  NA,  NA,  NA,  NA,  NA                     
1115,394, 327, 356, 408, 329, 385, 357, 357, NA,  NA

eventually, even to get rid of the rows with only NAs. I have tried 

data = sapply(data[,1], FUN=unlist)

and then 

data = sapply(data, '[', seq(max(sapply(data, length))))

but I keep getting a matrix with all the elements unlisted in one column. Please advise.

Solution

  • I guess the 'data' should be a list instead of a vector, then the code would work

    t(sapply(data, `length<-`, max(lengths(data))))

    NOTE: lengths is a faster option (introduced in the recent R versions) that replaces sapply(data, length)

    data

    data = list(
  c(349, 364, 393, 356, 357, 394, 334, 394, 343, 365, 349),
  c(390, 336, 752, 377),
  c(670, 757, 405, 343, 1109, 350, 372),
  c(0, 0),
  numeric(0),
  c(1115, 394, 327, 356, 408, 329, 385, 357, 357))