mode: New order statistic.

[pspp] / src / math / mode.h

diff --git a/src/math/mode.h b/src/math/mode.h
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+++ b/src/math/mode.h
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+/* 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 */