将列表列表中的所有 NULL 值替换为其他内容/具有不同长度的列表列表

Question

我有一个列表列表，我需要将其转换为相应的数据框。

行的位置很重要，这样我以后可以将它们链接到另一个项目。我尝试了一种将其放入数据框的方法，但由于某些行为 NULL，我不能这样做。

  first = c(1,2,3)
  second = c(1,2)
  problemrows = NULL

  mylist = list(first,second,problemrows)
  #mylist   - should turn into a dataframe with each row being same order as        the list of lists.  NULL value would be a null row

 library(plyr) # doesn't work because of NULLs above
    t(plyr::rbind.fill.matrix(lapply(mylist, t)))
  ## help^^^   Ideally the row that doesn't work would just be a null row or the new dataframe would remove these NULL lists as rows and instead assign appropriate row#s to everything else to make up for what was skipped.


     # other approach - change all the NULL list of lists to something like -999 which is another fix.

Answer 1

first = c(1,2,3)
second = c(1,2)
problemrows = NULL

mylist = list(first,second,problemrows)

mylist <- sapply(mylist, function(x) ifelse(x == "NULL", NA, x))

library(plyr) # doesn't work because of NULLs above
t(plyr::rbind.fill.matrix(lapply(mylist, t)))