R Language Lists Convert a list to a vector while keeping empty list elements
Example
When one wishes to convert a list to a vector or data.frame object empty elements are typically dropped.
This can be problematic which a list is created of a desired length are created with some empty values (e.g. a list with n elements is created to be added to an m x n matrix, data.frame, or data.table). It is possible to losslessly convert a list to a vector however, retaining empty elements:
res <- list(character(0), c("Luzhuang", "Laisu", "Peihui"), character(0),
c("Anjiangping", "Xinzhai", "Yongfeng"), character(0), character(0),
c("Puji", "Gaotun", "Banjingcun"), character(0), character(0),
character(0))
res
[[1]] character(0) [[2]] [1] "Luzhuang" "Laisu" "Peihui" [[3]] character(0) [[4]] [1] "Anjiangping" "Xinzhai" "Yongfeng" [[5]] character(0) [[6]] character(0) [[7]] [1] "Puji" "Gaotun" "Banjingcun" [[8]] character(0) [[9]] character(0) [[10]] character(0)
res <- sapply(res, function(s) if (length(s) == 0) NA_character_ else paste(s, collapse = " "))
res
[1] NA "Luzhuang Laisu Peihui" NA "Anjiangping Xinzhai Yongfeng" NA [6] NA "Puji Gaotun Banjingcun" NA NA NA
