Closes #2171 -- edge case missed in fix to #2032

NEWS.md

@@ -34,7 +34,7 @@
 
 7. Seg fault in `rbindlist()` when one or more items are empty, [#2019](https://github.com/Rdatatable/data.table/issues/2019). Thanks Michael Lang for the pull request.
 
-8. Error printing 0-length `ITime` objects, [#2032](https://github.com/Rdatatable/data.table/issues/2032). Thanks Michael Chirico for the pull request.
+8. Error printing 0-length `ITime` and `NA` objects, [#2032](https://github.com/Rdatatable/data.table/issues/2032) and [#2171](https://github.com/Rdatatable/data.table/issues/2171). Thanks Michael Chirico for the pull requests and @franknarf1 for pointing out a shortcoming of the initial fix.
 
 9. `as.IDate.POSIXct` error with `NULL` timezone, [#1973](https://github.com/Rdatatable/data.table/issues/1973). Thanks @lbilli for reporting and Michael Chirico for the pull request.
 

R/IDateTime.R

@@ -121,7 +121,10 @@ as.character.ITime <- format.ITime <- function(x, ...) {
     x  <- abs(unclass(x))
     hh <- x %/% 3600L
     mm <- (x - hh * 3600L) %/% 60L
-    ss <- trunc(x - hh * 3600L - 60L * mm)
+    # #2171 -- trunc gives numeric but %02d requires integer;
+    #   as.integer is also faster (but doesn't handle integer overflow)
+    #   http://stackoverflow.com/questions/43894077
+    ss <- as.integer(x - hh * 3600L - 60L * mm)
     res = sprintf('%02d:%02d:%02d', hh, mm, ss)
     # Fix for #1354, so that "NA" input is handled correctly.
     if (is.na(any(neg))) res[is.na(x)] = NA

inst/tests/tests.Rraw

@@ -9909,7 +9909,9 @@ ans = data.table(id=c(1L,3L),a=c(1,2))
 for (i in 1:100) test(1763, rbindlist(x, idcol="id"), ans)
 
 # as.ITime(character(0)) used to fail, #2032
-test(1764, capture.output(format(as.ITime(character(0)))), "character(0)")
+test(1764.1, format(as.ITime(character(0))), character(0))
+# Edge case from #2171
+test(1764.2, format(structure(NA_integer_, class = "ITime")), NA_character_)
 
 # IDateTime error when tzone is NULL, #1973
 x = as.POSIXct('2017-03-17')