From e6d9669bd7e54f75f1ef4b9767b8db390eb77b53 Mon Sep 17 00:00:00 2001
From: Sergio Correia <sergio.correia@gmail.com>
Date: Tue, 4 Apr 2017 00:15:21 -0400
Subject: [PATCH] Add -keepnone- option to join.ado

---
 README.md        |  2 +-
 src/fmerge.ado   |  9 ++++++++-
 src/fmerge.sthlp |  2 +-
 src/join.ado     |  7 ++++---
 src/join.sthlp   | 10 +++++++++-
 5 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index c22c0b1..77a149c 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # FTOOLS: A faster Stata for large datasets
 
-- Current version: `2.9.0 28mar2017`
+- Current version: `2.10.0 3apr2017`
 - Jump to: [`usage`](#usage) [`benchmarks`](#benchmarks) [`install`](#installation)
 
 -----------
diff --git a/src/fmerge.ado b/src/fmerge.ado
index 10deb38..f78c154 100644
--- a/src/fmerge.ado
+++ b/src/fmerge.ado
@@ -1,4 +1,4 @@
-*! version 2.9.0 28mar2017
+*! version 2.10.0 3apr2017
 * wrapper for join.ado, parsing code based on merge.ado
 
 program define fmerge 
@@ -36,11 +36,18 @@ program define fmerge
 
     loc uniquemaster = cond("`mtype'" == "1:1", "uniquemaster", "")
 
+    loc check = "`keepusing'"!=""
+    loc keepusing : list keepusing - varlist
+    if ("`keepusing'"=="" & `check') {
+      loc keepnone keepnone // don't keep any variable from using
+    }
+
     loc cmd join `keepusing', ///
     	from(`using') ///
     	by(`varlist') ///
     	keep(`keep') ///
     	assert(`assert') ///
+      `keepnone' ///
     	`generate' ///
     	`nogenerate' ///
     	`uniquemaster' ///
diff --git a/src/fmerge.sthlp b/src/fmerge.sthlp
index fe079a5..522b0f4 100644
--- a/src/fmerge.sthlp
+++ b/src/fmerge.sthlp
@@ -1,5 +1,5 @@
 {smcl}
-{* *! version 1.9.0 10jan2017}{...}
+{* *! version 2.10.0 3apr2017}{...}
 {vieweralsosee "ftools" "help ftools"}{...}
 {vieweralsosee "join" "help join"}{...}
 {vieweralsosee "[R] merge" "help merge"}{...}
diff --git a/src/join.ado b/src/join.ado
index 28ab7aa..ff3af10 100644
--- a/src/join.ado
+++ b/src/join.ado
@@ -1,10 +1,10 @@
-*! version 2.9.0 28mar2017
+*! version 2.10.0 3apr2017
 program define join
 
 // Parse --------------------------------------------------------------------
 
 	syntax ///
-		[anything]  /// Variables that will be added (default is _all)
+		[anything]  /// Variables that will be added (default is _all unless keepnone is used)
 		, ///
 		[from(string asis) into(string asis)] /// -using- dataset
 		[by(string)] /// Primary and foreign keys
@@ -13,6 +13,7 @@ program define join
 		[GENerate(name) NOGENerate] /// _merge variable
 		[UNIQuemaster] /// Assert that -by- is an id in the master dataset
 		[noLabel] ///
+		[KEEPNone] ///
 		[noNOTEs] ///
 		[noREPort] ///
 		[Verbose]
@@ -70,7 +71,7 @@ program define join
 		loc cmd `"qui use `if' using "`filename'", clear"'
 	}
 
-	if ("`anything'" != "") {
+	if ("`anything'" != "" | "`keepnone'"!=""}) {
 		keep `using_keys' `anything'
 	}
 	else {
diff --git a/src/join.sthlp b/src/join.sthlp
index 796efb7..e4b27d9 100644
--- a/src/join.sthlp
+++ b/src/join.sthlp
@@ -1,5 +1,5 @@
 {smcl}
-{* *! version 1.9.0 10jan2017}{...}
+{* *! version 2.10.0 3apr2017}{...}
 {vieweralsosee "ftools" "help ftools"}{...}
 {vieweralsosee "fmerge" "help fmerge"}{...}
 {vieweralsosee "[R] merge" "help merge"}{...}
@@ -71,6 +71,8 @@ As above, but with the "using" dataset currently open instead of the "master"
 {...}
 {synopt :{opt nonote:s}}do not copy notes from using{p_end}
 {...}
+{synopt :{opt keepn:one}}don't add any variables from using (overrides default of {it:_all}){p_end}
+{...}
 {synopt :{opt v:erbose}}show internal debug info
 {p_end}
 {synoptline}
@@ -172,6 +174,12 @@ above 100,000 observations (due to Mata's overhead).
     specifies that notes in the using dataset not be added to the 
     merged dataset; see {manhelp notes D:notes}.
 
+{phang}
+{cmd:keepnone}
+    specifies that no variables from using will be added. Use this in combination
+    with {cmd:keep(match)} if you just want to keep a group of observations
+    from the master dataset.
+
 {phang}
 {cmd:noreport}
     specifies that {cmd:join} not present its summary table of