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lib/Smokeping/RRDhelpers.pm

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+# -*- perl -*-
+package Smokeping::RRDhelpers;
+
+=head1 NAME
+
+Smokeping::RRDhelpers - Functions for doing 'interesting things' with RRDs.
+
+=head1 OVERVIEW
+
+This module holds a collection of functions for doing advanced calculations
+and effects on rrd files.
+
+=cut
+
+use strict;
+use RRDs;
+
+=head2 IMPLEMENTATION
+
+=head3 get_stddev(rrd,ds,cf,start,end[,step])
+
+Pull the data values off the rrd file and calculate the standard deviation. Nan
+values get ignored in this process.
+
+=cut
+
+sub get_stddev{
+    my $rrd = shift;
+    my $ds = shift;
+    my $cf = shift;
+    my $start = shift;
+    my $end = shift;
+    my $step = shift;
+    my ($realstart,$realstep,$names,$array) = RRDs::fetch $rrd, $cf, '--start',$start, '--end',$end,($step ? ('--resolution',$step):());
+    if (my $err = RRDs::error){
+        warn $err
+    };
+    my $idx = 0;
+    for (@$names){
+        last if $ds eq $_;
+        $idx ++;
+    }
+    my $sum = 0;
+    my $sqsum = 0;
+    my $cnt = 0;
+    foreach my $line (@$array){
+        my $val = $line->[$idx];
+        if (defined $val){
+            $cnt++;
+            $sum += $val;
+            $sqsum += $val**2;
+        }
+    }
+    return undef unless $cnt;
+    my $sqdev =  1.0 / $cnt * ( $sqsum - $sum**2 / $cnt );
+    return $sqdev < 0.0 ? 0.0 : sqrt($sqdev);
+}
+
+
+
+1;
+
+__END__
+
+=head1 COPYRIGHT
+
+Copyright 2007 by Tobias Oetiker
+
+=head1 LICENSE
+
+This program is free software; you can redistribute it
+and/or modify it under the terms of the GNU General Public
+License as published by the Free Software Foundation; either
+version 2 of the License, or (at your option) any later
+version.
+
+This program is distributed in the hope that it will be
+useful, but WITHOUT ANY WARRANTY; without even the implied
+warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+PURPOSE.  See the GNU General Public License for more
+details.
+
+You should have received a copy of the GNU General Public
+License along with this program; if not, write to the Free
+Software Foundation, Inc., 675 Mass Ave, Cambridge, MA
+02139, USA.
+
+=head1 AUTHOR
+
+Tobias Oetiker E<lt>tobi@oetiker.chE<gt>
+
+=cut