add tests and news.md

Author: Mukulyadav2004

NEWS.md

@@ -14,6 +14,8 @@
 
 3. `fread(keepLeadingZeros=TRUE)` now correctly parses dates with components with leading zeros as dates instead of strings, [#6851](https://github.com/Rdatatable/data.table/issues/6851). Thanks @TurnaevEvgeny for the report and @ben-schwen for the fix.
 
+4. `as.data.table()` now properly handles keys: explicitly specified keys are set, while unspecified keys are cleared (returning NULL from `key()`), [#6859](https://github.com/Rdatatable/data.table/issues/6859). Thanks @brookslogan for the report and @Mukulyadav2004 for the fix.
+
 ## NOTES
 
 1. Continued work to remove non-API C functions, [#6180](https://github.com/Rdatatable/data.table/issues/6180). Thanks Ivan Krylov for the PRs and for writing a clear and concise guide about the R API: https://aitap.codeberg.page/R-api/.

R/as.data.table.R

@@ -214,14 +214,13 @@ as.data.table.list = function(x,
 }
 
 as.data.table.data.frame = function(x, keep.rownames=FALSE, key=NULL, ...) {
-  if (is.data.table(x)) return(as.data.table.data.table(x,keep.rownames = keep.rownames, key = key, ...)) # S3 is weird, #6739. Also # nocov; this is tested in 2302.{2,3}, not sure why it doesn't show up in coverage.
+  if (is.data.table(x)) return(as.data.table.data.table(x, ...)) # S3 is weird, #6739. Also # nocov; this is tested in 2302.{2,3}, not sure why it doesn't show up in coverage.
   if (!identical(class(x), "data.frame")) return(as.data.table(as.data.frame(x), keep.rownames=keep.rownames, key=key, ...))
   if (!isFALSE(keep.rownames)) {
     # can specify col name to keep.rownames, #575; if it's the same as key,
     #   kludge it to 'rn' since we only apply the new name afterwards, #4468
     if (is.character(keep.rownames) && identical(keep.rownames, key)) key='rn'
-    ans = data.table(rn=rownames(x), x, keep.rownames=FALSE)
-    if (!is.null(key)) setkeyv(ans, key)
+    ans = data.table(rn=rownames(x), x, keep.rownames=FALSE, key=key)
     if (is.character(keep.rownames))
       setnames(ans, 'rn', keep.rownames[1L])
     return(ans)
@@ -246,18 +245,18 @@ as.data.table.data.frame = function(x, keep.rownames=FALSE, key=NULL, ...) {
   ans
 }
 
-as.data.table.data.table = function(x, keep.rownames = FALSE, key = NULL, ...) {
+as.data.table.data.table = function(x, keep.rownames, key, ...) {
   # as.data.table always returns a copy, automatically takes care of #473
   if (any(cols_with_dims(x))) { # for test 2089.2
-    return(as.data.table.list(x, keep.rownames = keep.rownames, key = key, ...))
+    return(as.data.table.list(x, keep.rownames = if(missing(keep.rownames)) FALSE else keep.rownames, key = if(missing(key)) NULL else key, ...))
   }
   x = copy(x) # #1681
   # fix for #1078 and #1128, see .resetclass() for explanation.
   setattr(x, 'class', .resetclass(x, "data.table"))
-  if (!is.null(key)) {
+  if (!missing(key)){
     setkeyv(x, key)
   } else {
-    setkeyv(x, NULL)
+    setattr(x, "sorted", NULL)
   }
   x
 }

inst/tests/tests.Rraw

@@ -21084,3 +21084,9 @@ test(2307, { capture.output(print(DT, class = TRUE, show.indices = TRUE)); TRUE
 dt = data.table(date=as.IDate(c(NA, "2014-12-05")))
 test(2308.01, fread("date\nNA\n2014-12-05", keepLeadingZeros=TRUE), dt)
 test(2308.02, fread("date\nNA\n2014-12-05", keepLeadingZeros=FALSE), dt)
+
+# Test that as.data.table.data.table preserves key when explicitly specified but not when omitted
+test(2309.01, data.frame(t = c(3:1,4:5), y = 1:5) %>% as.data.table(key = "t") %>% key(), "t")
+test(2309.02, tibble::tibble(t = c(3:1,4:5), y = 1:5) %>% as.data.table(key = "t") %>% key(), "t")
+test(2309.03, data.table(t = c(3:1,4:5), y = 1:5) %>% as.data.table(key = "t") %>% key(), "t")
+test(2309.04, data.table(t = c(3:1,4:5), key = "t") %>% as.data.table() %>% key(), NULL)

man/as.data.table.Rd

@@ -21,7 +21,7 @@ Functions to check if an object is \code{data.table}, or coerce it if possible.
 \usage{
 as.data.table(x, keep.rownames=FALSE, \dots)
 
-\method{as.data.table}{data.table}(x, keep.rownames=FALSE, key=NULL, \dots)
+\method{as.data.table}{data.table}(x, \dots)
 
 \method{as.data.table}{array}(x, keep.rownames=FALSE, key=NULL, sorted=TRUE,
               value.name="value", na.rm=TRUE, \dots)