mode: New order statistic.

diff --git a/src/math/automake.mk b/src/math/automake.mk
index 5237583b60500db5af7a1b2c7ed65124eccb3d26..fa9fb82ae7add7f4eae5ccf370401e85a31fb524 100644 (file)
--- a/src/math/automake.mk
+++ b/src/math/automake.mk
@@ -39,6 +39,7 @@ src_math_libpspp_math_la_SOURCES = \
        src/math/levene.c src/math/levene.h \
        src/math/linreg.c src/math/linreg.h \
        src/math/merge.c  src/math/merge.h \
+       src/math/mode.c src/math/mode.h \
        src/math/moments.c  src/math/moments.h \
        src/math/np.c src/math/np.h \
        src/math/order-stats.c src/math/order-stats.h \

diff --git a/src/math/mode.c b/src/math/mode.c
new file mode 100644 (file)
index 0000000..6c9f0c4
--- /dev/null
+++ b/src/math/mode.c
@@ -0,0 +1,66 @@
+/* PSPP - a program for statistical analysis.
+   Copyright (C) 2008, 2009, 2011, 2022 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>. */
+
+#include <config.h>
+
+#include "math/mode.h"
+
+#include "data/casereader.h"
+#include "data/val-type.h"
+#include "data/variable.h"
+#include "libpspp/assertion.h"
+#include "libpspp/cast.h"
+
+#include "gl/xalloc.h"
+
+
+static void
+mode_destroy (struct statistic *stat)
+{
+  struct mode *mode = UP_CAST (stat, struct mode, parent.parent);
+  free (mode);
+}
+
+static void
+mode_accumulate (struct statistic *stat, const struct ccase *cx UNUSED,
+                 double c, double cc UNUSED, double y)
+{
+  struct mode *mode = UP_CAST (stat, struct mode, parent.parent);
+  if (c > mode->mode_weight)
+    {
+      mode->mode = y;
+      mode->mode_weight = c;
+      mode->n_modes = 1;
+    }
+  else if (c == mode->mode_weight)
+    mode->n_modes++;
+}
+
+struct mode *
+mode_create (void)
+{
+  struct mode *mode = xmalloc (sizeof *mode);
+  *mode = (struct mode) {
+    .parent = {
+      .parent = {
+        mode_destroy,
+      },
+      .accumulate = mode_accumulate,
+    },
+    .mode = SYSMIS,
+  };
+  return mode;
+}

diff --git a/src/math/mode.h b/src/math/mode.h
new file mode 100644 (file)
index 0000000..b2d1441
--- /dev/null
+++ b/src/math/mode.h
@@ -0,0 +1,46 @@
+/* PSPP - a program for statistical analysis.
+   Copyright (C) 2004, 2008, 2009, 2022 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>. */
+
+#ifndef MATH_MODE_H
+#define MATH_MODE_H 1
+
+#include <stddef.h>
+
+#include "order-stats.h"
+
+/* To calculate the mode:
+
+   - Create a "struct mode" with mode_create().
+   - Feed in the data with order_stats_accumulate() or
+     order_stats_accumulate_idx().  The data must be in sorted order: if
+     necessary, use one of the sorting functions from sort.h to sort them.
+   - The members of "struct mode" then designate the mode.
+   - Destroy the data structure with statistic_destroy().
+*/
+
+struct mode
+{
+  struct order_stats parent;
+
+  /* These are initialized by order_stats_accumulate{_idx}(). */
+  double mode;          /* The value of the smallest mode, if 'n_modes' > 0. */
+  double mode_weight;   /* The weight of each mode, if 'n_modes' > 0. */
+  size_t n_modes;       /* The number of modes. */
+};
+
+struct mode *mode_create (void);
+
+#endif /* mode.h */