Perl Monk, Perl Meditation PerlMonks

### Re: Bag uniform distribution algorithms

by kcott (Chancellor)
 on Apr 26, 2013 at 09:02 UTC ( #1030794=note: print w/replies, xml ) Need Help??

in reply to Bag uniform distribution algorithms

G'day Dave,

By alternatively splicing elements from either end of the distribution, I get your original 'qw( A C B A D C A B C A )'.

```\$ perl -Mstrict -Mwarnings -E '
my %bag = ( A => 4, B => 2, C => 3, D => 1 );
my @distribution;

for my \$key (sort { \$bag{\$b} <=> \$bag{\$a} } keys %bag) {
my \$base_offset = int(@distribution / (\$bag{\$key} + 1));
my \$offset = \$base_offset;

for (1 .. \$bag{\$key}) {
next unless \$_ % 2;
splice @distribution, \$offset, 0, \$key;

if (\$_ < \$bag{\$key}) {
splice @distribution, -\$offset, 0, \$key;
}

\$offset += \$base_offset + 1;
}
}

say "@distribution";
'
A C B A D C A B C A

If I round up the \$base_offset value, the middle two elements are reversed but everything else remains the same. I don't see this as being more or less uniform but maybe it's more correct.

```\$ perl -Mstrict -Mwarnings -E '
my %bag = ( A => 4, B => 2, C => 3, D => 1 );
my @distribution;

for my \$key (sort { \$bag{\$b} <=> \$bag{\$a} } keys %bag) {
my \$base_offset = int(@distribution / (\$bag{\$key} + 1) + 0.5);
+
my \$offset = \$base_offset;

for (1 .. \$bag{\$key}) {
next unless \$_ % 2;
splice @distribution, \$offset, 0, \$key;

if (\$_ < \$bag{\$key}) {
splice @distribution, -\$offset, 0, \$key;
}

\$offset += \$base_offset + 1;
}
}

say "@distribution";
'
A C B A C D A B C A

I haven't done extensive testing on this solution. Beyond your sample input, I tried:

```my %bag = ( A => 4, B => 2, C => 3, D => 1, Z => 1 );

gives: A C B A C D Z A B C A; and

```my %bag = ( A => 4, B => 2, C => 3, D => 1, Y => 5, Z => 1 );

gives: Y A C Y B A C Z D Y A B Y C A Y; and

```my %bag = ( A => 4, B => 2, C => 3, D => 1, X => 6, Y => 5, Z => 1 );

gives: X Y A X C Y B A X Y Z D C X A B Y C X A Y X; and

```my %bag = ( A => 4, B => 2, C => 3, D => 1, W => 4, X => 6, Y => 5, Z
+=> 1 );

gives: X Y A W X C Y B A W X Y Z D C X W A B Y C X W A Y X

The above 4 tests all included rounding; without rounding, the results are:

```A C B A Z D C A B C A
Y A C Y B A C D Z Y A B Y C A Y
X Y A C X Y B A C X D Z Y X A B Y X C A Y X
X Y A W C X Y B A W C X D Z Y X W A B Y X C W A Y X

-- Ken

Create A New User
Node Status?
node history
Node Type: note [id://1030794]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others avoiding work at the Monastery: (6)
As of 2018-10-23 10:24 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
When I need money for a bigger acquisition, I usually ...

Results (125 votes). Check out past polls.

Notices?