Closes #590. fread gains 'key' argument.

R/fread.R

@@ -1,5 +1,5 @@
 
-fread <- function(input="",sep="auto",sep2="auto",nrows=-1L,header="auto",na.strings="NA",stringsAsFactors=FALSE,verbose=getOption("datatable.verbose"),autostart=1L,skip=0L,select=NULL,drop=NULL,colClasses=NULL,integer64=getOption("datatable.integer64"),dec=if (sep!=".") "." else ",", col.names, check.names=FALSE, encoding="unknown", quote="\"", strip.white=TRUE, fill=FALSE, blank.lines.skip=FALSE, showProgress=getOption("datatable.showProgress"),data.table=getOption("datatable.fread.datatable")) {
+fread <- function(input="",sep="auto",sep2="auto",nrows=-1L,header="auto",na.strings="NA",stringsAsFactors=FALSE,verbose=getOption("datatable.verbose"),autostart=1L,skip=0L,select=NULL,drop=NULL,colClasses=NULL,integer64=getOption("datatable.integer64"),dec=if (sep!=".") "." else ",", col.names, check.names=FALSE, encoding="unknown", quote="\"", strip.white=TRUE, fill=FALSE, blank.lines.skip=FALSE, key=NULL, showProgress=getOption("datatable.showProgress"),data.table=getOption("datatable.fread.datatable")) {
     if (!is.character(dec) || length(dec)!=1L || nchar(dec)!=1) stop("dec must be a single character e.g. '.' or ','")
     # handle encoding, #563
     if (length(encoding) != 1L || !encoding %in% c("unknown", "UTF-8", "Latin-1")) {
@@ -130,5 +130,13 @@ fread <- function(input="",sep="auto",sep2="auto",nrows=-1L,header="auto",na.str
     # FR #768
     if (!missing(col.names))
         setnames(ans, col.names) # setnames checks and errors automatically
+    if (!is.null(key) && data.table) {
+        if (!is.character(key)) 
+            stop("key argument of data.table() must be character")
+        if (length(key) == 1L) {
+            key = strsplit(key, split = ",")[[1L]]
+        }
+        setkeyv(ans, key)
+    }
     ans
 }

README.md

@@ -43,6 +43,8 @@
 
   14. `fread` gains `fill` argument with default `FALSE` for backwards compatibility. Closes [#536](https://github.com/Rdatatable/data.table/issues/536).
 
+  15. `fread` gains `key` argument, [#590](https://github.com/Rdatatable/data.table/issues/590).
+
 #### BUG FIXES
 
   1. Now compiles and runs on IBM AIX gcc. Thanks to Vinh Nguyen for investigation and testing, [#1351](https://github.com/Rdatatable/data.table/issues/1351).

inst/tests/tests.Rraw

@@ -7268,6 +7268,10 @@ text="x,y\n1,a\n2,b\n"
 test(1586.1, fread(text, colClasses=c("integer", "factor")), data.table(x=1:2, y=factor(letters[1:2])))
 test(1586.2, fread(text, colClasses=c(x="factor")), data.table(x=factor(1:2), y=letters[1:2]))
 
+# FR #590
+text="x,y\n2,a\n1,q\n3,c\n"
+test(1587, fread(text, key="y"), setDT(fread(text), key="y"))
+
 ##########################
 
 # TODO: Tests involving GForce functions needs to be run with optimisation level 1 and 2, so that both functions are tested all the time.

man/fread.Rd

@@ -15,7 +15,7 @@ skip=0L, select=NULL, drop=NULL, colClasses=NULL,
 integer64=getOption("datatable.integer64"),         # default: "integer64"
 dec=if (sep!=".") "." else ",", col.names, 
 check.names=FALSE, encoding="unknown", quote="\"", 
-strip.white=TRUE, fill=FALSE, blank.lines.skip=FALSE, 
+strip.white=TRUE, fill=FALSE, blank.lines.skip=FALSE, key=NULL, 
 showProgress=getOption("datatable.showProgress"),   # default: TRUE
 data.table=getOption("datatable.fread.datatable")   # default: TRUE
 )
@@ -43,6 +43,7 @@ data.table=getOption("datatable.fread.datatable")   # default: TRUE
   \item{strip.white}{ default is \code{TRUE}. Strips leading and trailing whitespaces of unquoted fields. If \code{FALSE}, only header trailing spaces are removed. }
   \item{fill}{logical (default is \code{FALSE}). If \code{TRUE} then in case the rows have unequal length, blank fields are implicitly filled.}
   \item{blank.lines.skip}{\code{logical}, default is \code{FALSE}. If \code{TRUE} blank lines in the input are ignored.}
+  \item{key}{Character vector of one or more column names which is passed to \code{\link{setkey}}. 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")}. Only valid when argument \code{data.table=TRUE}.}
   \item{showProgress}{ TRUE displays progress on the console using \code{\\r}. It is produced in fread's C code where the very nice (but R level) txtProgressBar and tkProgressBar are not easily available. }
   \item{data.table}{ TRUE returns a \code{data.table}. FALSE returns a \code{data.frame}. }
 }