FACTOR: Ensure a non-zero number of factors.

Before attempting to perform factor analysis, check
that the number of factors is greater than zero.
Issue an appropriate warning if this is not the case.

diff --git a/src/language/stats/factor.c b/src/language/stats/factor.c
index 706e1d0d3b06e28b7b3a7affcfa79dabb175d39d..72a066408bb9f09e95fd863acaf40fe88888a332 100644 (file)
--- a/src/language/stats/factor.c
+++ b/src/language/stats/factor.c
@@ -542,6 +542,9 @@ cmd_factor (struct lexer *lexer, struct dataset *ds)
                              PV_NO_DUPLICATE | PV_NUMERIC))
     goto error;
 
+  if (factor.n_vars < 2)
+    msg (MW, _("Factor analysis on a single variable is not useful."));
+
   while (lex_token (lexer) != '.')
     {
       lex_match (lexer, '/');
@@ -986,7 +989,7 @@ static void
 show_factor_matrix (const struct cmd_factor *factor, struct idata *idata, const gsl_matrix *fm)
 {
   int i;
-  const int n_factors = n_extracted_factors (factor, idata);
+  const int n_factors = idata->n_extractions;
 
   const int heading_columns = 1;
   const int heading_rows = 2;
@@ -1205,7 +1208,7 @@ show_explained_variance (const struct cmd_factor * factor, struct idata *idata,
 
       if (factor->print & PRINT_EXTRACTION)
        {
-         if ( i < n_extracted_factors (factor, idata))
+         if (i < idata->n_extractions)
            {
              /* Sums of squared loadings */
              tab_double (t, c++, i + heading_rows, 0, e_lambda, NULL);
@@ -1457,12 +1460,20 @@ do_factor (const struct cmd_factor *factor, struct casereader *r)
   gsl_eigen_symmv_sort (idata->eval, idata->evec, GSL_EIGEN_SORT_ABS_DESC);
 #endif
 
+  idata->n_extractions = n_extracted_factors (factor, idata);
+
+  if (idata->n_extractions == 0)
+    {
+      msg (MW, _("The FACTOR criteria result in zero factors extracted. Therefore no analysis will be performed."));
+      goto finish;
+    }
+    
   {
     const gsl_vector *extracted_eigenvalues = NULL;
     gsl_vector *initial_communalities = gsl_vector_alloc (factor->n_vars);
     gsl_vector *extracted_communalities = gsl_vector_alloc (factor->n_vars);
     size_t i;
-    struct factor_matrix_workspace *fmw = factor_matrix_workspace_alloc (idata->msr->size, n_extracted_factors (factor, idata));
+    struct factor_matrix_workspace *fmw = factor_matrix_workspace_alloc (idata->msr->size, idata->n_extractions);
     gsl_matrix *factor_matrix = gsl_matrix_calloc (factor->n_vars, fmw->n_factors);
 
     if ( factor->extraction == EXTRACTION_PAF)
@@ -1501,10 +1512,9 @@ do_factor (const struct cmd_factor *factor, struct casereader *r)
       }
     else if (factor->extraction == EXTRACTION_PC)
       {
-       for (i = 0 ; i < factor->n_vars; ++i)
-         {
-           gsl_vector_set (initial_communalities, i, communality (idata, i, factor->n_vars));
-         }
+       for (i = 0; i < factor->n_vars; ++i)
+         gsl_vector_set (initial_communalities, i, communality (idata, i, factor->n_vars));
+
        gsl_vector_memcpy (extracted_communalities, initial_communalities);
 
        iterate_factor_matrix (analysis_matrix, extracted_communalities, factor_matrix, fmw);
@@ -1523,6 +1533,8 @@ do_factor (const struct cmd_factor *factor, struct casereader *r)
     gsl_vector_free (extracted_communalities);
   }
 
+ finish:
+
   idata_free (idata);
 
   casereader_destroy (r);