cbind on null.dt to non-null.dt now works, closes #3445

NEWS.md

@@ -50,6 +50,8 @@
 
 17. Non-UTF8 strings were not always sorted correctly on Windows (a regression in v1.12.0), [#3397](https://github.com/Rdatatable/data.table/issues/3397) [#3451](https://github.com/Rdatatable/data.table/issues/3451). Thanks to @shrektan for reporting and fixing.
 
+18. `cbind` with a null (0-column) `data.table` now works as expected, [#3445](https://github.com/Rdatatable/data.table/issues/3445). Thanks to @mb706 for reporting.
+
 #### NOTES
 
 1. When upgrading to 1.12.0 some Windows users might have seen `CdllVersion not found` in some circumstances. We found a way to catch that so the [helpful message](https://twitter.com/MattDowle/status/1084528873549705217) now occurs for those upgrading from versions prior to 1.12.0 too, as well as those upgrading from 1.12.0 to a later version. See item 1 in notes section of 1.12.0 below for more background.

R/data.table.R

@@ -56,16 +56,16 @@ data.table <-function(..., keep.rownames=FALSE, check.names=FALSE, key=NULL, str
   .Call(CcopyNamedInList,x)   # to maintain pre-Rv3.1.0 behaviour, for now. See test 548.2. TODO: revist
   # TODO Something strange with NAMED on components of `...` to investigate. Or, just port data.table() to C.
 
-  n <- length(x)
-  if (n < 1L)
+  if (length(x) < 1L)
     return( null.data.table() )
   # fix for #5377 - data.table(null list, data.frame and data.table) should return null data.table. Simple fix: check all scenarios here at the top.
   if (identical(x, list(NULL)) || identical(x, list(list())) ||
       identical(x, list(data.frame(NULL))) || identical(x, list(data.table(NULL)))) return( null.data.table() )
   nd = name_dots(...)
+  if (any(nocols<-sapply(x, NCOL)==0L)) { tt=!nocols; x=x[tt]; nd=lapply(nd,'[',tt); }  # data.table(data.table(), data.table(a=integer())), #3445
   vnames = nd$vnames
-  # We will use novname later to know which were explicitly supplied in the call.
-  novname = nd$novname
+  novname = nd$novname  # novname used later to know which were explicitly supplied in the call
+  n <- length(x)
   if (length(vnames) != n) stop("logical error in vnames")   # nocov
   # cast to a list to facilitate naming of columns with dimension --
   #   unlist() at the end automatically handles the need to "push" names

R/utils.R

@@ -6,7 +6,7 @@
 #   identical(TRUE,x)
 # See PR#3421 for timings.
 # It was changed in R so that isTRUE(c(a=TRUE)) returned TRUE: https://github.com/wch/r-source/commit/828997ac6ecfb73aaa0aae9d1d0584a4ffc50881#diff-b41e3f9f1d389bb6f7a842cd5a3308b8
-if (base::getRversion() < "3.5.0") {  
+if (base::getRversion() < "3.5.0") {
   isTRUE  = function(x) is.logical(x) && length(x)==1L && !is.na(x) && x    # backport R's new implementation of isTRUE
   isFALSE = function(x) is.logical(x) && length(x)==1L && !is.na(x) && !x   # backport isFALSE that was added in R 3.5.0
 }

inst/tests/tests.Rraw

@@ -13856,6 +13856,13 @@ if (.Platform$OS.type == 'windows') local({
   Sys.setlocale('LC_CTYPE', lc_ctype)
 })
 
+# cbind of zero-row data.table with empty data.table messed up columns, #3445
+test(2012.1, data.table(data.table(), data.table(a=integer())), data.table(a=integer()))
+test(2012.2, data.table(data.frame(), data.table(a=integer())), data.table(a=integer()))
+test(2012.3, data.table(data.frame(), data.frame(a=integer())), data.table(a=integer()))
+dt = as.data.table(iris)
+test(2012.4, cbind(data.table(), dt[0]), dt[0])
+
 
 ###################################
 #  Add new tests above this line  #