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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
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