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Cookbook patch by Yuriy Kaminskiy

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This commit is contained in:
Kenichi Ishigaki 2011-09-06 15:21:20 +00:00
parent dd05ef54fd
commit d30f3ab459
1 changed files with 20 additions and 27 deletions
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47
lib/DBD/SQLite/Cookbook.pod
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@ -42,7 +42,7 @@ adapted from an example implementation in pysqlite.
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($x - $mu)**2;
$sigma += ($v - $mu)**2;
}
$sigma = $sigma / ($n - 1);
@ -66,41 +66,38 @@ expense of precision:
package variance2;
my $sum = 0;
my $count = 0;
my %hash;
sub new { bless [], shift; }
sub new { bless {sum => 0, count=>0, hash=> {} }, shift; }
sub step {
my ( $self, $value ) = @_;
my $hash = $self->{hash};
# by truncating and hashing, we can comsume many more data points
$value = int($value); # change depending on need for precision
# use sprintf for arbitrary fp precision
if (defined $hash{$value}) {
$hash{$value}++;
if (exists $hash->{$value}) {
$hash->{$value}++;
} else {
$hash{$value} = 1;
$hash->{$value} = 1;
}
$sum += $value;
$count++;
$self->{sum} += $value;
$self->{count}++;
}
sub finalize {
my $self = $_[0];
# Variance is NULL unless there is more than one row
return undef unless $count > 1;
return undef unless $self->{count} > 1;
# calculate avg
my $mu = $sum / $count;
my $mu = $self->{sum} / $self->{count};
my $sigma = 0;
foreach my $h (keys %hash) {
$sigma += (($h - $mu)**2) * $hash{$h};
while (my ($h, $v) = each %{$self->{hash}}) {
$sigma += (($h - $mu)**2) * $v;
}
$sigma = $sigma / ($count - 1);
$sigma = $sigma / ($self->{count} - 1);
return $sigma;
}
@ -115,25 +112,21 @@ The function can then be used as:
A third variable implementation, designed for arbitrarily large data sets:
package variance;
package variance3;
my $mu = 0;
my $count = 0;
my $S = 0
sub new { bless [], shift; }
sub new { bless {mu=>0, count=>0, S=>0}, shift; }
sub step {
my ( $self, $value ) = @_;
$count++;
$delta = $value - $mu;
$mu = $mu + $delta/$count
$S = $S + $delta*($value - $mu);
$self->{count}++;
my $delta = $value - $self->{mu};
$self->{mu} += $delta/$self->{count};
$self->{S} += $delta*($value - $self->{mu});
}
sub finalize {
my $self = $_[0];
return $S / ($count - 1);
return $self->{S} / ($self->{count} - 1);
}
The function can then be used as: