update description , news.md and add tests

Author: Mukulyadav2004

NEWS.md

@@ -42,6 +42,8 @@
 
 8. `groupingsets()` gets a new argument `enclos` for use together with the `jj` argument in functions wrapping `groupingsets()`, including the existing wrappers `rollup()` and `cube()`, [#5560](https://github.com/Rdatatable/data.table/issues/5560). When forwarding a `j`-expression as `groupingsets(jj = substitute(j))`, make sure to pass `enclos = parent.frame()` as well, so that the `j`-expression will be evaluated in the right context. This makes it possible for `j` to refer to variables outside the `data.table`. Thanks @sindribaldur for the report and @aitap for the fix.
 
+9. `data.table()` and `as.data.table()` with `keep.rownames=TRUE` now extract row names from named vectors, matching `data.frame()` behavior. Names from the first named vector in the input are used to create the row names column (default name `"rn"` or custom name via `keep.rownames="column_name"`), [#1916](https://github.com/Rdatatable/data.table/issues/1916). Thanks to @richierocks for the feature request and @Mukulyadav2004 for the implementation.
+
 ### BUG FIXES
 
 1. Custom binary operators from the `lubridate` package now work with objects of class `IDate` as with a `Date` subclass, [#6839](https://github.com/Rdatatable/data.table/issues/6839). Thanks @emallickhossain for the report and @aitap for the fix.

inst/tests/tests.Rraw

@@ -21420,3 +21420,9 @@ test(2330.5, as.data.table(data.frame(y, x), keep.rownames=TRUE), data.table(rn=
 
 DF <- data.frame(row.names = letters[1:6], V = 1:6)     # Test data.frame with explicit rownames
 test(2330.6, as.data.table(list(a = 6:1, DF), keep.rownames=TRUE), data.table(rn=letters[1:6], a=6:1, V=1:6))
+
+z <- setNames(1:3, rep("", 3))  # vector with all-empty names     # behaviour with all-empty row names
+test(2330.7, as.data.table(list(z), keep.rownames=TRUE), data.table(rn=rep("", 3), V1=1:3))
+
+M <- matrix(1:6, nrow=3, dimnames=list(rep("", 3), c("V1", "V2")))   #  test of list(M) for empty-rowname'd matrix input
+test(2330.8, as.data.table(list(M), keep.rownames=TRUE), data.table(rn=rep("", 3), V1=1:3, V2=4:6))

man/as.data.table.Rd

@@ -31,7 +31,7 @@ is.data.table(x)
 }
 \arguments{
   \item{x}{An R object.}
-  \item{keep.rownames}{Default is \code{FALSE}. If \code{TRUE}, adds the input object's names as a separate column named \code{"rn"}. \code{keep.rownames = "id"} names the column \code{"id"} instead.}
+  \item{keep.rownames}{Default is \code{FALSE}. If \code{TRUE}, adds the input object's names as a separate column named \code{"rn"}. \code{keep.rownames = "id"} names the column \code{"id"} instead. For lists and when calling \code{data.table()}, names from the first named vector are extracted and used as row names, similar to \code{data.frame()} behavior.}
   \item{key}{ Character vector of one or more column names which is passed to \code{\link{setkeyv}}. }
   \item{sorted}{logical used in \emph{array} method, default \code{TRUE} is overridden when \code{key} is provided. }
   \item{value.name}{character scalar used in \emph{array} method, default \code{"value"}.}