checking to see if a hash has data

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: checking to see if a hash has data by brian_d_foy (Abbot) on May 14, 2005 at 00:00 UTC
If you want a count of the keys, use the keys() operator in scalar context. `my $key_total = keys %hash;` [download] If you need something else, such as the count of the defined values, you have to do a bit more work. `my $defined_count = grep { defined } values %hash;` [download] -- brian d foy <brian@stonehenge.com>	[reply] [d/l] [select]
Re: checking to see if a hash has data by holli (Abbot) on May 13, 2005 at 23:58 UTC
Would if (!%hash) {} work? Yes. Or use `scalar keys %hash` to get the number of entries. holli, /regexed monk/	[reply] [d/l]
Re: checking to see if a hash has data by tlm (Prior) on May 14, 2005 at 00:25 UTC
You just go ahead and try it from the command line (make sure that warnings are enabled): `% perl -wle 'my %foo; if ( %foo ) { print "OK" } else { print "KO" }' KO % perl -wle 'my %foo = (1,2); if ( %foo ) { print "OK" } else { print +"KO" }' OK` [download] But you have to be careful, because sometimes perl will conjure keys from thin air. For example: `% perl -wl print( %foo ? "OK" : "KO" ); my @bar = grep $_, @foo{ 1, 2, 3 }; print( %foo ? "OK" : "KO" ); ^D KO OK` [download] Notice how the second test succeeded, even though we never initialized `%foo`. For this reason, maybe something like this (also proposed by brian_d_foy) would be better: `if ( grep defined, values %foo ) { # etc. }` [download] This test will succeed only if `%foo` contains at least one defined value. the lowliest monk	[reply] [d/l] [select]
Re: checking to see if a hash has data by borisz (Canon) on May 14, 2005 at 00:51 UTC
`if ( () = keys %hash ) { # has data } else { # no data }` [download] Boris	[reply] [d/l]