How to convert a list of lists to a dataframe - non-identical lists

Question

I have a list where each element is a named list, but the elements are not the same everywhere. I have read solutions on how to convert lists of lists to dataframes here and

Answer 1

Any function using data.frame(.) on each element of the list before binding would be terribly inefficient (not to mention unnecessary). Here's another way using data.table's rbindlist (from v1.9.3) which you can get here.

require(data.table) ## 1.9.3
rbindlist(lisnotOK, fill=TRUE)
#     a b     c    d
# 1:  1 2    hi   NA
# 2: NA 2 hello nope

It works on list-of-lists (as in this question), data.frames and data.tables.

If not this, then I'd go with Ananda's list2mat function (if your types are all identical).

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Benchmarks on Ananda's L2 data:

fun1 <- function(inList) ldply(inList, as.data.frame)
fun2 <- function(inList) list2mat(inList)
fun3 <- function(inList) rbindlist(inList, fill=TRUE)
fun4 <- function(inList) rbind_all(lapply(inList, as.data.frame))

microbenchmark(fun1(L2), fun2(L2), fun3(L2), fun4(L2), times = 10)
# Unit: milliseconds
#      expr         min          lq      median          uq         max neval
#  fun1(L2) 1927.857847 2161.432665 2221.999940 2276.241366 2366.649614    10
#  fun2(L2)   12.039652   12.167613   12.361629   12.483751   16.040885    10
#  fun3(L2)    1.225929    1.374395    1.473621    1.510876    1.858597    10
#  fun4(L2) 1435.153576 1457.053482 1492.334965 1548.547706 1630.443430    10

Note: I've used as.data.frame(.) instead of data.frame(.) (former is slightly faster).