Closes #1066. .SDcols understands "!".

R/data.table.R

@@ -890,7 +890,7 @@ chmatch2 <- function(x, table, nomatch=NA_integer_) {
                     # FR #4979 - negative numeric and character indices for SDcols
                     colsub = substitute(.SDcols)
                     # fix for #5190. colsub[[1L]] gave error when it's a symbol.
-                    if (is.call(colsub) && colsub[[1L]] == "-") {
+                    if (is.call(colsub) && deparse(colsub[[1L]], 500L) %in% c("!", "-")) {
                         colm = TRUE
                         .SDcols = eval(colsub[[2L]], parent.frame(), parent.frame())
                     } else colm = FALSE

README.md

@@ -40,6 +40,8 @@
 
   13. `melt.data.table` also retains attributes wherever possible. Closes [#702](https://github.com/Rdatatable/data.table/issues/702) and [#993](https://github.com/Rdatatable/data.table/issues/993). Thanks to @richierocks for the report.
 
+  14. `.SDcols` understands `!` now, i.e., `DT[, .SD, .SDcols=!"a"]` now works, and is equivalent to `DT[, .SD, .SDcols = -c("a")]`. Closes [#1066](https://github.com/Rdatatable/data.table/issues/1066). 
+
 #### BUG FIXES
 
   1. `if (TRUE) DT[,LHS:=RHS]` no longer prints, [#869](https://github.com/Rdatatable/data.table/issues/869). Tests added. To get this to work we've had to live with one downside: if a `:=` is used inside a function with no `DT[]` before the end of the function, then the next time `DT` is typed at the prompt, nothing will be printed. A repeated `DT` will print. To avoid this: include a `DT[]` after the last `:=` in your function. If that is not possible (e.g., it's not a function you can change) then `print(DT)` and `DT[]` at the prompt are guaranteed to print. As before, adding an extra `[]` on the end of `:=` query is a recommended idiom to update and then print; e.g. `> DT[,foo:=3L][]`. Thanks to Jureiss for reporting.

inst/tests/tests.Rraw

@@ -6110,6 +6110,10 @@ test(1494.2, rbind(DT2, DT1), error="Class attributes at column")
 DT = data.table(year=2010:2014, v1=runif(5), v2=1:5, v3=letters[1:5])
 test(1496, DT[, shift(v1, 1:2, NA, "lead", TRUE)], DT[, shift(.SD, 1:2, NA, "lead", TRUE), .SDcols=2L])
 
+# Fix for #1066
+DT = data.table(x=1, y=2, z=3, a=4, b=5, c=6)
+test(1497, DT[, .SD, .SDcols = !c("a", "c")], DT[, !c("a", "c"), with=FALSE])
+
 ##########################