Add sum_sqr_sample_weights methods

The SampleWeighted data can be considered as
run length encoded individual samples, for which
each individual sample has a weight of 1.

lib/Statistics/Descriptive/PDL.pm

@@ -29,6 +29,7 @@ my @cache_methods = qw /
   geometric_mean harmonic_mean
   max min sample_range
   iqr
+  sum_sqr_sample_weights
 /;
 __PACKAGE__->_make_caching_accessors( \@cache_methods );
 
@@ -62,7 +63,7 @@ sub _make_caching_accessors {
             };
         };
     }
- 
+
     return;
 }
 
@@ -179,6 +180,11 @@ sub sum_sqr_weights {
     return $self->count;
 }
 
+sub _sum_sqr_sample_weights {
+    my $self = shift;
+    return $self->sum_sqr_weights;
+}
+
 sub _min {
     my $self = shift;
     return $self->_get_piddle->min;

lib/Statistics/Descriptive/PDL/SampleWeighted.pm

@@ -163,6 +163,12 @@ sub _percentile {
     return $piddle->at($idx);
 }
 
+#  weight for each sample is 1
+sub _sum_sqr_sample_weights {
+    my $self = shift;
+    return $self->sum_weights;
+}
+
 
 
 1;
@@ -227,6 +233,12 @@ Add data to the stats object.  Appends to any existing data.
 Same as L<Statistics::Descriptive::PDL::Weighted> except that non-integer weights
 will be converted to integer using PDL's rules.
 
+=item sum_sqr_sample_weights
+
+Same as the C< sum_weights > method.  This is because one can consider each
+value as weighted by the number of samples, where each individual sample has
+a weight of 1.
+
 =back
 
 =head1 AUTHOR

lib/Statistics/Descriptive/PDL/Weighted.pm

@@ -510,6 +510,10 @@ Sum of the weights vector.
 
 Sum of the squared weights vector.  Each weight is squared and the sum of these values then calculated.
 
+=item sum_sqr_sample_weights
+
+Same as the C< sum_sqr_weights > method.
+
 =item Statistical methods
 
 Most of the methods should need no explanation here,

t/descr_weighted.t

@@ -536,6 +536,7 @@ sub test_data_with_samples {
 
     is ($stats->sum_weights, 150, 'sum of weights correct');
     is ($stats->sum_sqr_weights, 100+400+900+1600+2500, 'sum of weights correct');
+    is ($stats->sum_sqr_sample_weights, 100+400+900+1600+2500, 'sum of weights correct');
 
 }
 

t/sample_weighted.t

@@ -102,6 +102,10 @@ sub test_wikipedia_percentile_example {
     is $weighted->percentile(50), $weighted->median,   "median same as 50th percentile, " . join ' ', @data;
     is $weighted->percentile(50), $unweighted->median, 'weighted and unweighted median';
 
+    is $weighted->sum_sqr_sample_weights,
+        $unweighted->sum_sqr_sample_weights,
+        'weighted and unweighted sum of squared sample weights';
+
     #  no longer guaranteed unless dedup is inplace
     # ok $weighted->values_are_unique, "unique flag set to true value after calculating percentiles";