Closes #1352. merge() handles ignores names in by argument.

R/merge.R

@@ -36,6 +36,7 @@ merge.data.table <- function(x, y, by = NULL, by.x = NULL, by.y = NULL, all = FA
             stop("A non-empty vector of column names for `by` is required.")
         if (!all(by %in% intersect(colnames(x), colnames(y))))
             stop("Elements listed in `by` must be valid column names in x and y")
+        by = unname(by)
         by.x = by.y = by
     }
     # with i. prefix in v1.9.3, this goes away. Left here for now ...

README.md

@@ -23,6 +23,8 @@
 
   3. `last()` dispatches `xts::last()` properly again, [#1347](https://github.com/Rdatatable/data.table/issues/1347). Thanks to @JoshuaUlrich for spotting and suggesting the fix.
 
+  4. `merge.data.table` ignores names when `by` argument is a named vector, [#1352](https://github.com/Rdatatable/data.table/issues/1352). Thanks @sebastian-c.
+
 #### NOTES
 
 

inst/tests/tests.Rraw

@@ -6960,6 +6960,12 @@ if (!"package:xts" %in% search()) {
     test(1559.2, last(.xts(1:3,1:3)), .xts(1:3, 1:3)[3, ])
 }
 
+# fix for #1352
+dt1 = data.table(a=1:5, b=6:10, c=11:15)
+dt2 = data.table(a=3:6, b=8:11, d=1L)
+by_cols = c(x="a", y="b")
+test(1560, merge(dt1,dt2, by=by_cols, sort=FALSE), dt1[dt2, nomatch=0L, on=unname(by_cols)])
+
 ##########################