Closes #842. as.data.table.list correctly handles first element NULL.

R/data.table.R

@@ -1684,17 +1684,27 @@ as.data.table.list <- function(x, keep.rownames=FALSE, ...) {
  n = vapply(x, length, 0L)
  mn = max(n)
  x = copy(x)
- if (any(n<mn)) 
- for (i in which(n<mn)) {
- if (!is.null(x[[i]])) {# avoids warning when a list element is NULL
- # Implementing FR #4813 - recycle with warning when nr %% nrows[i] != 0L
- if (!n[i] && mn)
- warning("Item ", i, " is of size 0 but maximum size is ", mn, ", therefore recycled with 'NA'")
- else if (n[i] && mn %% n[i] != 0)
- warning("Item ", i, " is of size ", n[i], " but maximum size is ", mn, " (recycled leaving a remainder of ", mn%%n[i], " items)")
- x[[i]] = rep(x[[i]], length.out=mn)
+ idx = which(n < mn)
+ if (length(idx)) {
+ for (i in idx) {
+ if (!is.null(x[[i]])) {# avoids warning when a list element is NULL
+ # Implementing FR #4813 - recycle with warning when nr %% nrows[i] != 0L
+ if (!n[i] && mn)
+ warning("Item ", i, " is of size 0 but maximum size is ", mn, ", therefore recycled with 'NA'")
+ else if (n[i] && mn %% n[i] != 0)
+ warning("Item ", i, " is of size ", n[i], " but maximum size is ", mn, " (recycled leaving a remainder of ", mn%%n[i], " items)")
+ x[[i]] = rep(x[[i]], length.out=mn)
+ }
  }
  }
+ # fix for #842
+ if (mn > 0L) {
+ nz = which(n > 0L)
+ xx = point(vector("list", length(nz)), seq_along(nz), x, nz)
+ if (!is.null(names(x)))
+ setattr(xx, 'names', names(x)[nz])
+ x = xx
+ }
  if (is.null(names(x))) setattr(x,"names",paste("V",seq_len(length(x)),sep=""))
  setattr(x,"row.names",.set_row_names(max(n)))
  setattr(x,"class",c("data.table","data.frame"))

README.md

@@ -129,6 +129,8 @@
 
  36. Issues on merges involving `factor` columns with `NA` and merging `factor` with `character` type with non-identical levels are both fixed. Closes [#499](https://github.com/Rdatatable/data.table/issues/499) and [#945](https://github.com/Rdatatable/data.table/issues/945). Thanks to @AbielReinhart and @stewbasic for the minimal examples.
 
+ 37. `as.data.table(ll)` returned a `data.table` with 0-rows when the first element of the list has 0-length, for e.g., `ll = list(NULL, 1:2, 3:4)`. This is now fixed by removing those 0-length elements. Closes [#842](https://github.com/Rdatatable/data.table/issues/842). Thanks to @Rick for the nice minimal example.
+
 #### NOTES
 
  1. Clearer explanation of what `duplicated()` does (borrowed from base). Thanks to @matthieugomez for pointing out. Closes [#872](https://github.com/Rdatatable/data.table/issues/872).

inst/tests/tests.Rraw

@@ -5955,6 +5955,15 @@ test(1483.3, merge(x,y,by="country",all=T), data.table(country=factor(c("US", "U
 setkey(y)
 test(1483.4, y[x], data.table(country=factor("US"), key="country"))
 
+# Fix for #842
+SomeFunction <- function(x, setnull=1L) {
+ ans <- replicate(length(x), list("bla1", "bla2"), simplify=FALSE)
+ ans[setnull] <- list(NULL)
+ return(ans)
+}
+DT <- data.table(ID=1:3, key="ID")
+test(1484, DT[, SomeFunction(ID, setnull=1L)], DT[, SomeFunction(ID, setnull=2L)])
+
 ##########################