Closes #1023. Preserve attributes in gsum and gmean.

README.md

@@ -32,7 +32,7 @@
 
   9. `rbindlist` gains `idcol` argument which can be used to generate an index column. If `idcol=TRUE`, the column is automatically named `.id`. Instead you can also provide a column name directly. If the input list has no names, indices are automatically generated. Closes [#591](https://github.com/Rdatatable/data.table/issues/591). Also thanks to @KevinUshey for filing [#356](https://github.com/Rdatatable/data.table/issues/356).
 
-  10. A new helper function `uniqueN` is now implemented. It is equivalent to `length(unique(x))` but much faster. It accepts `atomic vectors`, `data.frames` and `data.tables` as input and returns the number of unique rows. For example, DT[, .(uN = uniqueN(.SD)), by=x]` returns the number of unique rows within each group of `x`.
+  10. A new helper function `uniqueN` is now implemented. It is equivalent to `length(unique(x))` but much faster. It accepts `atomic vectors`, `data.frames` and `data.tables` as input and returns the number of unique rows. For example, DT[, .(uN = uniqueN(.SD)), by=x]` returns the number of unique rows within each group of `x`. Thanks to @DavidArenburg as well for the FR.
 
 #### BUG FIXES
 
@@ -113,6 +113,8 @@
 
   29. Fixed two segfaults in `shift()` when number of rows in `x` is lesser than value for `n`. Closes [#1009](https://github.com/Rdatatable/data.table/issues/1009) and [#1014](https://github.com/Rdatatable/data.table/issues/1014). Thanks to @jangorecki and @ashinm for the reproducible reports.
 
+  30. Attributes are preserved for `sum()` and `mean()` when fast internal (GForce) implementations are used. Closes [#1023](https://github.com/Rdatatable/data.table/issues/1023). Thanks to @DavidArenburg for the nice reproducible example.
+
 #### NOTES
 
   1. Clearer explanation of what `duplicated()` does (borrowed from base). Thanks to @matthieugomez for pointing out. Closes [#872](https://github.com/Rdatatable/data.table/issues/872).

inst/tests/tests.Rraw

@@ -5869,6 +5869,10 @@ DT <- data.table(A = rep(1:3, each=4), B = rep(1:4, each=3), C = rep(1:2, 6))
 test(1475.1, uniqueN(DT), 10L)
 test(1475.2, DT[, .(uN=uniqueN(.SD)), by=A], data.table(A=1:3, uN=c(3L,4L,3L)))
 
+# preserve class attribute in GForce mean (and sum)
+DT <- data.table(x = rep(1:3, each = 3), y = as.Date(seq(Sys.Date(), (Sys.Date() + 8), by = "day")))
+test(1476.1, DT[, .(y=mean(y)), x], setDT(aggregate(y ~ x, DT, mean)))
+
 ##########################
 
 

src/gsumm.c

@@ -95,6 +95,7 @@ SEXP gsum(SEXP x, SEXP narm)
         error("Type '%s' not supported by GForce sum (gsum). Either add the prefix base::sum(.) or turn off GForce optimization using options(datatable.optimize=1)", type2char(TYPEOF(x)));
     }
     free(s);
+    copyMostAttrib(x, ans);
     UNPROTECT(1);
     // Rprintf("this gsum took %8.3f\n", 1.0*(clock()-start)/CLOCKS_PER_SEC);
     return(ans);
@@ -163,6 +164,7 @@ SEXP gmean(SEXP x, SEXP narm)
         else REAL(ans)[i] = (double)s[i];
     }
     free(s); free(c);
+    copyMostAttrib(x, ans);
     UNPROTECT(1);
     // Rprintf("this gmean na.rm=TRUE took %8.3f\n", 1.0*(clock()-start)/CLOCKS_PER_SEC);
     return(ans);