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., 59 Temple Place - Suite 330, Boston, MA
32 #include "debug-print.h"
34 /* The two different types of samples. */
37 TYPE_A_FROM_B, /* 5 FROM 10 */
38 TYPE_FRACTION /* 0.5 */
41 /* SAMPLE transformation. */
45 int type; /* One of TYPE_*. */
46 int n, N; /* TYPE_A_FROM_B: n from N. */
47 int m, t; /* TYPE_A_FROM_B: # picked so far; # so far. */
48 unsigned frac; /* TYPE_FRACTION: a fraction of UINT_MAX. */
51 static trns_proc_func sample_trns_proc;
56 struct sample_trns *trns;
62 if (!lex_force_num ())
64 if (!lex_integer_p ())
67 if (tokval <= 0 || tokval >= 1)
69 msg (SE, _("The sampling factor must be between 0 and 1 "
74 frac = tokval * UINT_MAX;
82 if (!lex_force_match_id ("FROM"))
84 if (!lex_force_int ())
89 msg (SE, _("Cannot sample %d observations from a population of "
99 trns = xmalloc (sizeof *trns);
100 trns->h.proc = sample_trns_proc;
105 trns->m = trns->t = 0;
107 add_transformation ((struct trns_header *) trns);
109 return lex_end_of_command ();
112 /* Executes a SAMPLE transformation. */
114 sample_trns_proc (struct trns_header * trns, struct ccase *c UNUSED,
117 struct sample_trns *t = (struct sample_trns *) trns;
120 if (t->type == TYPE_FRACTION)
122 if (rng_get_unsigned (pspp_rng ()) <= t->frac)
131 U = rng_get_double (pspp_rng ());
132 if ((t->N - t->t) * U >= t->n - t->m)