src/data/casereader-project.c

   1 /* PSPP - a program for statistical analysis.
   2    Copyright (C) 2009, 2011 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
  16
  17 #include <config.h>
  18
  19 #include "data/casereader-provider.h"
  20 #include "data/subcase.h"
  21
  22 #include "gl/xalloc.h"
  23
  24 static bool
  25 projection_is_no_op (const struct casereader *reader, const struct subcase *sc)
  26 {
  27   size_t n = subcase_get_n_fields (sc);
  28   size_t i;
  29
  30   if (n != caseproto_get_n_widths (casereader_get_proto (reader)))
  31     return false;
  32
  33   for (i = 0; i < n; i++)
  34     if (subcase_get_case_index (sc, i) != i)
  35       return false;
  36
  37   return true;
  38 }
  39
  40 struct casereader_project
  41   {
  42     struct subcase old_sc;
  43     struct subcase new_sc;
  44   };
  45
  46 static struct ccase *
  47 project_case (struct ccase *old, void *project_)
  48 {
  49   const struct casereader_project *project = project_;
  50   struct ccase *new = case_create (subcase_get_proto (&project->new_sc));
  51   subcase_copy (&project->old_sc, old, &project->new_sc, new);
  52   case_unref (old);
  53   return new;
  54 }
  55
  56 static bool
  57 destroy_projection (void *project_)
  58 {
  59   struct casereader_project *project = project_;
  60   subcase_uninit (&project->old_sc);
  61   subcase_uninit (&project->new_sc);
  62   free (project);
  63   return true;
  64 }
  65
  66 /* Returns a casereader in which each row is obtained by extracting the subcase
  67    SC from the corresponding row of SUBREADER. */
  68 struct casereader *
  69 casereader_project (struct casereader *subreader, const struct subcase *sc)
  70 {
  71   if (projection_is_no_op (subreader, sc))
  72     return casereader_rename (subreader);
  73   else
  74     {
  75       struct casereader_project *project = xmalloc (sizeof *project);
  76       const struct caseproto *proto;
  77
  78       subcase_clone (&project->old_sc, sc);
  79       proto = subcase_get_proto (&project->old_sc);
  80
  81       subcase_init_empty (&project->new_sc);
  82       subcase_add_proto_always (&project->new_sc, proto);
  83
  84       static const struct casereader_translator_class class = {
  85         project_case, destroy_projection,
  86       };
  87
  88       return casereader_translate_stateless (subreader, proto,
  89                                              &class, project);
  90     }
  91 }
  92
  93 /* Returns a casereader in which each row is obtained by extracting the value
  94    with index COLUMN from the corresponding row of SUBREADER. */
  95 struct casereader *
  96 casereader_project_1 (struct casereader *subreader, int column)
  97 {
  98   const struct caseproto *subproto = casereader_get_proto (subreader);
  99   struct casereader *reader;
 100   struct subcase sc;
 101
 102   subcase_init (&sc, column, caseproto_get_width (subproto, column),
 103                 SC_ASCEND);
 104   reader = casereader_project (subreader, &sc);
 105   subcase_uninit (&sc);
 106
 107   return reader;
 108 }
 109