1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
|
# -*- 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;
return sqrt( 1.0 / $cnt * ( $sqsum - $sum**2 / $cnt ))
}
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
|
