Initial version of interaction

[pspp-builds.git] / src / math / interaction.c

diff --git a/src/math/interaction.c b/src/math/interaction.c
new file mode 100644 (file)
index 0000000..be3d3ed
--- /dev/null
+++ b/src/math/interaction.c
@@ -0,0 +1,103 @@
+/* PSPP - Creates data structures to store interactions for
+   statistical routines.  
+
+   Copyright (C) 2007 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 2 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, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA. */
+
+/*
+  An interaction is a gsl_vector containing a "product" of other
+  variables. The variables can be either categorical or numeric.
+  If the variables are all numeric, the interaction is just the
+  scalar product. If any of the variables are categorical, their
+  product is a vector containing 0's in all but one entry. This entry
+  is found by combining the vectors corresponding to the variables'
+  OBS_VALS member. If there are K categorical variables, each with
+  N_1, N_2, ..., N_K categories, then the interaction will have
+  N_1 * N_2 * N_3 *...* N_K - 1 entries.
+ */
+#include <assert.h>
+#include <libpspp/alloc.h>
+#include <gsl/gsl_math.h>
+#include <gsl/gsl_vector.h>
+#include <data/category.h>
+#include <data/variable.h>
+
+/*
+  Convert a list of values to a binary vector. The order of VALS must
+  correspond to the order of V.
+ */
+gsl_vector *
+get_interaction (union value **vals, const struct variable **v, size_t n_vars)
+{
+  gsl_vector *result = NULL;
+  size_t *subs = NULL;
+  size_t length = 1;
+  size_t i;
+  size_t j;
+  double tmp = 1.0;
+
+  assert (n_vars > 0);
+  for (i = 0; i < n_vars; i++)
+    {
+      if (var_is_alpha (v[i]))
+       {
+         length *= cat_get_n_categories (v[i]);
+       }
+      else
+       {
+         length = (length > 0) ? length : 1;
+       }
+    }
+  if (length > 0)
+    {
+      length--;
+    }
+
+  result = gsl_vector_calloc (length);
+  subs = xnmalloc (n_vars, sizeof (*subs));
+  for (j = 0; j < n_vars; j++)
+    {
+      if (var_is_alpha (v[j]))
+       {
+         subs[j] = cat_value_find (v[j], vals[j]);
+       }
+    }
+  j = subs[0];
+  for (i = 1; i < n_vars; i++)
+    {
+      j = j * cat_get_n_categories (v[i]) + subs[i];
+    }
+  gsl_vector_set (result, j, 1.0);
+  /*
+     If any of the variables are numeric, the interaction of that
+     variable with another is just a scalar product.
+   */
+  for (i = 1; i < n_vars; i++)
+    {
+      if (var_is_numeric (v[i]))
+       {
+         tmp *= vals[i]->f;
+       }
+    }
+  if (fabs (tmp - 1.0) > GSL_DBL_EPSILON)
+    {
+      gsl_vector_set (result, j, tmp);
+    }
+  free (subs);
+
+  return result;
+}