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Perl: the Markov chain saw

Re^4: Merge hash into another hash

by linuxer (Curate)
on Jul 17, 2009 at 09:13 UTC ( #780973=note: print w/replies, xml ) Need Help??

in reply to Re^3: Merge hash into another hash
in thread Merge hash into another hash

Hi, let me try to explain with my limited knowledge of perl's internal behaviour ;o)

Your solution converts %target and %source into flat lists, combines it to one list and assigns that list to %target...

Grandfather's solution only inserts the key-value pairs from %source into %target, overwriting already existing pairs.

This is less expensive than converting into lists and reassigning these lists.

I tried a benchmark which shows that Grandfather's solution is faster than yours.

I have to admit, that - until this post - I preferred and used the way you presented (mainly because of readability), but now I have to reconsider ;o)

#!/usr/bin/perl # vim: set ts=4 sw=4 et sta: use strict; use warnings; use Benchmark qw( cmpthese ); my %target; my %source; ## prefill @target{'aa'..'zz' } = 'aa' .. 'zz'; @source{'ww'..'yy', 1..100} = ( 'ww'..'yy', 1..100 ); cmpthese( -1, { grandfather => sub { my %t = %target; @t{keys %source} = values %source; }, sleepyjay => sub { my %t = %target; %t = ( %t, %source ); }, }); __END__ Rate sleepyjay grandfather sleepyjay 598/s -- -62% grandfather 1585/s 165% -- Rate sleepyjay grandfather sleepyjay 649/s -- -62% grandfather 1706/s 163% --

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[atcroft]: abner: Do you mean something like SELECT `foo`, `bar` FROM `table_name' WHERE (( `foo` = "asdf" ) OR ( `bar` = 'asdw' )); Or something else?
[abner]: yes. i am familiar with mysql but ignorant about how to get around the fact that placeholders can only represent single scalar values.
[abner]: my $sth = $dbh->prepare(' SELECT * FROM charge WHERE cpt = ?') or die "Couldn't prepare statement: " . $dbh->errstr;
[abner]: what if i want SELECT * FROM charge WHERE col1 = x and col2 = y?

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