Dear Stat Monks,

I am a fool, and strictly this problem is not perl, but lack of statistical knowledge. I apologise for that... I present the following simplest of problems:

vmstat 1 10 extract:
po fr
0  0
0  0
150  10
0  0
0  0

[download]
I wish to calculate the ratio po:fr for this. If it exceeds 15:1, make some printf noise. My current solution is:


my $tlsamples = @series_po; # = @series_fr
return 0 if ($tlsamples == 0);
my $sum_po = sum(\@series_po); # = 150
my $sum_fr = sum(\@series_fr); # = 10
 
$sum_fr = 1 if ($sum_fr == 0);
my $avg_po = $sum_po / $tlsamples; # =150 / 5 = 30
my $avg_fr = $sum_fr / $tlsamples; # = 10 / 5 = 2

$avg_fr = 1 (if $avg_fr == 0); # avoid div/0
my $pofr = $avg_po / $avg_fr; # = 15

[download]

This result of 15:1, is the same as for the following series:

po  fr
150 10

[download]

The problem is, I need the zeroes to be significant in the first series, since they are. A single value spike should not be able to cause an alert, given many other zero values! (where 0 = no activity in vmstat context)

I have zero (pun intended) statistical background. I have thought of substituting each zero value to its nearest least-signicant alternative e.g.

po fr
150 10
1 1
1 1
1 1
1 1

[download]

In this case the ratio works out to (154/5) / (14/5) = 11. Is there a correct statistical perl-friendly approach that provides significance to the zeroes in the series?

Niel

In reply to A lesson in statistics by 0xbeef

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