retain timezones on CJ()

NEWS.md

@@ -51,6 +51,9 @@
 
 14. `fread()`'s rare `Internal error: Sampling jump point 10 is before the last jump ended` has been fixed, [#2157](https://github.com/Rdatatable/data.table/issues/2157). Thanks to Frank Erickson and Artem Klevtsov for reporting with example files which are now added to the test suite.
 
+15. `CJ()` no longer loses attribute information, [#2029](https://github.com/Rdatatable/data.table/issues/2029). Thanks to @MarkusBonsch and @royalts for the pull request.
+
+
 #### NOTES
 
 1. `?data.table` makes explicit the option of using a `logical` vector in `j` to select columns, [#1978](https://github.com/Rdatatable/data.table/issues/1978). Thanks @Henrik-P for the note and @MichaelChirico for filing.

R/setkey.R

@@ -330,11 +330,11 @@ CJ <- function(..., sorted = TRUE, unique = FALSE)
     if (unique) l = lapply(l, unique)
 
     dups = FALSE # fix for #1513
-    # using rep.int instead of rep speeds things up considerably (but attributes are dropped).
-    j = lapply(l, class)  # changed "vapply" to avoid errors with "ordered" "factor" input
     if (length(l)==1L && sorted && length(o <- forderv(l[[1L]])))
         l[[1L]] = l[[1L]][o]
     else if (length(l) > 1L) {
+        # using rep.int instead of rep speeds things up considerably (but attributes are dropped).
+        attribs = lapply(l, attributes)  # remember attributes for resetting after rep.int
         n = vapply(l, length, 0L)
         nrow = prod(n)
         x = c(rev(take(cumprod(rev(n)))), 1L)
@@ -351,8 +351,9 @@ CJ <- function(..., sorted = TRUE, unique = FALSE)
                 l[[i]] = rep.int(y, times = nrow/(x[i]*n[i]))
             else
                 l[[i]] = rep.int(rep.int(y, times = rep.int(x[i], n[i])), times = nrow/(x[i]*n[i]))
-            if (any(class(l[[i]]) != j[[i]]))
-                setattr(l[[i]], 'class', j[[i]]) # reset "Date" class - rep.int coerces to integer
+            if (!is.null(attribs[[i]])){
+                attributes(l[[i]]) <- attribs[[i]] # reset all attributes that were destroyed by rep.int
+            }
         }
     }
     setattr(l, "row.names", .set_row_names(length(l[[1L]])))

inst/tests/tests.Rraw

@@ -9974,6 +9974,53 @@ test(1770.6, fread(f)[256,V64], "0ABC")
 test(1770.7, fread(f, skip="spam"), error="not found in input")
 unlink(f)
 
+# CJ retains attributes and classes, #2029, PR#2150
+
+l <- list(a = as.POSIXct(c("2016-01-01", "2017-01-01"), tz = "UTC"),
+          b = as.POSIXct(c("2016-01-01", "2017-01-01")),
+          c = as.Date("2015-01-01"), ## according to comment about CJ loosing date class
+          d = factor(c("a", "b", "c"), ordered = TRUE), ## according to comment about bug with ordered factors
+          e = factor(c("a", "b", "c"), ordered = FALSE),
+          f = c(1,2),
+          g = c("a", "b"),
+          h = c(TRUE, FALSE))
+setattr(l$g, "test", "testval")## add hand-made attribute
+
+test(1771.1, lapply(l, attributes), lapply(do.call(CJ, l), attributes))
+test(1771.2, lapply(l, class), lapply(do.call(CJ, l), class))
+
+l <- list(a = factor(c("a", "b", "c"), ordered = TRUE),
+          b = as.POSIXct(c("2016-01-01", "2017-01-01")),
+          c = as.Date("2015-01-01"),
+          d = factor(c("a", "b", "c"), ordered = TRUE),
+          e = as.POSIXct(c("2016-01-01", "2017-01-01"), tz = "UTC"),
+          f = c(1,2),
+          g = c("a", "b"),
+          h = c(TRUE, FALSE))
+
+
+test(1771.3, lapply(l, attributes), lapply(do.call(CJ, l), attributes))
+test(1771.4, lapply(l, class), lapply(do.call(CJ, l), class))
+
+l <- list(a = factor(c("a", "b", "c"), ordered = TRUE),
+          b = as.POSIXct(c("2016-01-01", "2017-01-01")),
+          c = as.Date("2015-01-01"),
+          d = factor(c("a", "b", "c"), ordered = TRUE),
+          e = c(TRUE, FALSE),
+          f = c(1,2),
+          g = c("a", "b"),
+          h = as.POSIXct(c("2016-01-01", "2017-01-01"), tz = "UTC"))
+
+test(1771.5, lapply(l, attributes), lapply(do.call(CJ, l), attributes))
+test(1771.6, lapply(l, class), lapply(do.call(CJ, l), class))
+
+l <- list(a = NA,
+          c = c(1,2),
+          d = as.POSIXct("2016-01-01", tz = "UTC"))
+
+test(1771.7, lapply(l, attributes), lapply(do.call(CJ, l), attributes))
+test(1771.8, lapply(l, class), lapply(do.call(CJ, l), class))
+
 
 ##########################