1 /* PSPP - computes sample statistics.
2 Copyright (C) 1997-9, 2000 Free Software Foundation, Inc.
3 Written by Ben Pfaff <blp@gnu.org>.
5 This program is free software; you can redistribute it and/or
6 modify it under the terms of the GNU General Public License as
7 published by the Free Software Foundation; either version 2 of the
8 License, or (at your option) any later version.
10 This program is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software
17 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
21 #include <gsl/gsl_rng.h>
35 #define _(msgid) gettext (msgid)
37 #include "debug-print.h"
39 /* The two different types of samples. */
42 TYPE_A_FROM_B, /* 5 FROM 10 */
43 TYPE_FRACTION /* 0.5 */
46 /* SAMPLE transformation. */
49 int type; /* One of TYPE_*. */
50 int n, N; /* TYPE_A_FROM_B: n from N. */
51 int m, t; /* TYPE_A_FROM_B: # picked so far; # so far. */
52 unsigned frac; /* TYPE_FRACTION: a fraction of UINT_MAX. */
55 static trns_proc_func sample_trns_proc;
56 static trns_free_func sample_trns_free;
61 struct sample_trns *trns;
67 if (!lex_force_num ())
69 if (!lex_is_integer ())
71 unsigned long min = gsl_rng_min (get_rng ());
72 unsigned long max = gsl_rng_max (get_rng ());
75 if (tokval <= 0 || tokval >= 1)
77 msg (SE, _("The sampling factor must be between 0 and 1 "
82 frac = tokval * (max - min) + min;
90 if (!lex_force_match_id ("FROM"))
92 if (!lex_force_int ())
97 msg (SE, _("Cannot sample %d observations from a population of "
107 trns = xmalloc (sizeof *trns);
111 trns->m = trns->t = 0;
113 add_transformation (sample_trns_proc, sample_trns_free, trns);
115 return lex_end_of_command ();
118 /* Executes a SAMPLE transformation. */
120 sample_trns_proc (void *t_, struct ccase *c UNUSED,
123 struct sample_trns *t = t_;
126 if (t->type == TYPE_FRACTION)
128 if (gsl_rng_get (get_rng ()) <= t->frac)
129 return TRNS_CONTINUE;
131 return TRNS_DROP_CASE;
135 return TRNS_DROP_CASE;
137 U = gsl_rng_uniform (get_rng ());
138 if ((t->N - t->t) * U >= t->n - t->m)
141 return TRNS_DROP_CASE;
147 return TRNS_CONTINUE;
152 sample_trns_free (void *t_)
154 struct sample_trns *t = t_;