From 360a2f3d08842333922fe921316553e55e8394c3 Mon Sep 17 00:00:00 2001
From: John Darrington <john@darrington.wattle.id.au>
Date: Thu, 18 Dec 2003 04:25:59 +0000
Subject: [PATCH] Added a calculation of mode to FREQUENCIES

---
 src/ChangeLog           |  3 +++
 src/frequencies.q       | 28 +++++++++++++++++++++++-----
 tests/command/weight.sh |  6 +++---
 3 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 92e0b769..0beccd0f 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,6 @@
+Thu Dec 18 12:27:03 WAST 2003 John Darrington <john@darrington.wattle.id.au>
+        * added a calculation of the mode to FREQUENCIES
+
 Wed Dec 17 12:53:01 WAST 2003 John Darrington <john@darrington.wattle.id.au>
 
 	* moved (un)defs of DEBUGGING to config.h
diff --git a/src/frequencies.q b/src/frequencies.q
index 0ad5cf9d..477eee07 100644
--- a/src/frequencies.q
+++ b/src/frequencies.q
@@ -1057,13 +1057,31 @@ static void
 calc_stats (struct variable * v, double d[frq_n_stats])
 {
   double W = v->p.frq.tab.valid_cases;
-  double X_bar, M2, M3, M4;
+  double X_bar, X_mode, M2, M3, M4;
   struct freq *f;
+  int most_often;
 
-  /* Calculate the mean. */
+  /* Calculate the mean and  mode */
   X_bar = 0.0;
+  most_often = -1;
+  X_mode = SYSMIS;
   for (f = v->p.frq.tab.valid; f < v->p.frq.tab.missing; f++)
-    X_bar += f->v.f * f->c;
+    {
+      /* mean */
+      X_bar += f->v.f * f->c;
+
+      /* mode */
+      if (most_often < f->c ) 
+	{ 
+	  most_often=f->c;
+	  X_mode= f->v.f;
+	}
+      else if ( most_often == f->c ) 
+	{
+	  /* if there are 2 values , then mode is undefined */
+	  X_mode=SYSMIS;
+	}
+    }
   X_bar /= W;
 
   /* Calculate moments about the mean. */
@@ -1083,9 +1101,9 @@ calc_stats (struct variable * v, double d[frq_n_stats])
   /* Formulas below are taken from _SPSS Statistical Algorithms_. */
   d[frq_min] = v->p.frq.tab.valid[0].v.f;
   d[frq_max] = v->p.frq.tab.missing[-1].v.f;
-  d[frq_mode] = 0.0;
+  d[frq_mode] = X_mode;
   d[frq_range] = d[frq_max] - d[frq_min];
-  d[frq_median] = 0.0;
+  d[frq_median] = SYSMIS;
   d[frq_mean] = X_bar;
   d[frq_sum] = X_bar * W;
   d[frq_variance] = M2 / (W - 1);
diff --git a/tests/command/weight.sh b/tests/command/weight.sh
index 35bbaa77..6446c344 100755
--- a/tests/command/weight.sh
+++ b/tests/command/weight.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-# This program tests ....
+# This program tests the WEIGHT command
 
 TEMPDIR=/tmp/pspp-tst-$$
 
@@ -147,8 +147,8 @@ diff -B -b $TEMPDIR/pspp.list - <<EOF
 
 Mean         31.515
 S.E. Mean      .405
-Median         .000
-Mode           .000
+Median            .
+Mode         21.000
 Std Dev      10.937
 Variance    119.608
 Kurtosis      2.411
-- 
2.30.2