Closes #1571. Not joins along with mult='first'/'last' is handled pro…

…perly.

R/data.table.R

@@ -627,7 +627,7 @@ chmatch2 <- function(x, table, nomatch=NA_integer_) {
                 }
             }
             # Implementation for not-join along with by=.EACHI, #604
-            if (notjoin && byjoin) {
+	    if (notjoin && (byjoin || mult != "all")) { # mult != "all" needed for #1571 fix
                 notjoin = FALSE
                 if (verbose) {last.started.at=proc.time()[3];cat("not-join called with 'by=.EACHI'; Replacing !i with i=setdiff(x,i) ...");flush.console()}
                 orignames = copy(names(i))

README.md

@@ -140,6 +140,8 @@
 
   39. `roll` argument handles -ve integer64 values correctly, [#1405](https://github.com/Rdatatable/data.table/issues/1405). Thanks @bryan4887.
 
+  40. Not join along with `mult="first"` and `mult="last"` is handled correctly, [#1571](https://github.com/Rdatatable/data.table/issues/1571).
+
 #### NOTES
 
   1. Updated error message on invalid joins to reflect the new `on=` syntax, [#1368](https://github.com/Rdatatable/data.table/issues/1368). Thanks @MichaelChirico.

inst/tests/tests.Rraw

@@ -7611,6 +7611,13 @@ if ("package:bit64" %in% search()) {
     test(1614.4, dt[.(val), roll=-Inf, on="x", rollends=TRUE], ans[, y:=c(5,10,10)])
 }
 
+# fix for #1571
+x = data.table(c(1,1,2,7,2,3,4,4,7), 1:9)
+y = data.table(c(2,3,4,4,4,5))
+test(1615.1, x[!y, on="V1", mult="first"], data.table(V1=c(1,7), V2=INT(c(1,4))))
+test(1615.2, x[!y, on="V1", mult="last"], data.table(V1=c(1,7), V2=INT(c(2,9))))
+test(1615.3, x[!y, on="V1", mult="all"], data.table(V1=c(1,1,7,7), V2=INT(c(1,2,4,9))))
+
 ##########################
 
 # TODO: Tests involving GForce functions needs to be run with optimisation level 1 and 2, so that both functions are tested all the time.