Closes #1121. setDT gains 'key' argument.

R/data.table.R

@@ -2385,7 +2385,7 @@ setDF <- function(x) {
  invisible(x)
 }
 
-setDT <- function(x, keep.rownames=FALSE) {
+setDT <- function(x, keep.rownames=FALSE, key=NULL) {
  name = substitute(x)
  if (is.name(name)) {
  home <- function(x, env) {
@@ -2440,6 +2440,7 @@ setDT <- function(x, keep.rownames=FALSE) {
  } else {
  stop("Argument 'x' to 'setDT' should be a 'list', 'data.frame' or 'data.table'")
  }
+ if (!is.null(key)) setkeyv(x, key)
  if (is.name(name)) {
  name = as.character(name)
  assign(name, x, parent.frame(), inherits=TRUE)

README.md

@@ -58,6 +58,8 @@
 
  19. `as.data.table.*` and `setDT` argument `keep.rownames` can take a column name as well. When `keep.rownames=TRUE`, the column will still automatically named `rn`. Closes [#575](https://github.com/Rdatatable/data.table/issues/575). 
 
+ 20. `setDT` gains a `key` argument so that `setDT(X, key="a")` would convert `X` to a `data.table` by reference *and* key by the columns specified. Closes [#1121](https://github.com/Rdatatable/data.table/issues/1121).
+
 #### 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

@@ -6307,6 +6307,10 @@ if ("package:bit64" %in% search()) {
  test(1512.6, dt[.(as.integer64(2))], dt[.(2L)])
 }
 
+# setDT gains key argument, #1121
+X = list(a = 4:1, b=runif(4))
+test(1513, setkey(as.data.table(X), a), setDT(X, key="a"))
+
 ##########################
 
 

man/setDT.Rd

@@ -8,11 +8,12 @@
 
 }
 \usage{
-setDT(x, keep.rownames=FALSE)
+setDT(x, keep.rownames=FALSE, key=NULL)
 }
 \arguments{
  \item{x}{ A named or unnamed \code{list}, \code{data.frame} or \code{data.table}. }
  \item{keep.rownames}{ For \code{data.frame}s, \code{TRUE} retains the \code{data.frame}'s row names under a new column \code{rn}. }
+ \item{key}{Character vector of one or more column names which is passed to \code{\link{setkeyv}}. It may be a single comma separated string such as \code{key="x,y,z"}, or a vector of names such as \code{key=c("x","y","z")}. }
 }
 
 \details{
@@ -43,6 +44,10 @@ setDT(X)
 # don't provide names
 X = list(a=1:4, letters[1:4])
 setDT(X, FALSE)
+
+# setkey directly
+X = list(a = 4:1, b=runif(4))
+setDT(X, key="a")[]
 }
 \keyword{ data }