Initializing a hash using conditions

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

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Re: Initializing a hash using conditions by dave_the_m (Monsignor) on Feb 03, 2005 at 12:04 UTC
if is a statement modifier, so you can't use it there. Try something like: `$i ? () : ('abc' => 7)` [download] which inserts either zero or two elements into the list of key-value pairs, depending on the condition. Dave.	[reply] [d/l]
Re: Initializing a hash using conditions by Anonymous Monk on Feb 03, 2005 at 12:06 UTC
`%hash = ( $i ? (abc => 7) : (), hk => 5, jk => 6, );` [download]	[reply] [d/l]
Re^2: Initializing a hash using conditions by Random_Walk (Prior) on Feb 03, 2005 at 13:19 UTC
Anon Monk++, nice neat solution that does not create the key abc unless the condition evaluates true. However I think you switched the logic of the OP `# OP %hash = ( ('abc' => 7) if (! $i), # abc if not $i 'hk' => 5, 'jk' => 6 # Anonymonk %hash = ( $i ? (abc => 7) : (), # create abc if $i hk => 5, jk => 6, ); # /me thinks %hash = ( $i ? () : (abc => 7), # create abc if not $i hk => 5, jk => 6, );` [download] Cheers, R. Pereant, qui ante nos nostra dixerunt!	[reply] [d/l]
Re: Initializing a hash using conditions by holli (Abbot) on Feb 03, 2005 at 12:04 UTC
`%hash = ( 'abc' => $i ? 7 : 0, 'hk' => 5, 'jk' => 6 );` [download] see perlop holli, regexed monk	[reply] [d/l]
Re: Initializing a hash using conditions by monkey_boy (Priest) on Feb 03, 2005 at 12:03 UTC
Maybe, dont know to be honest, but what you wrote wont compile. For simplicity , why not just do this... `my $i = 1; my %hash = ( 'hk' => 5, 'jk' => 6 ); $hash{'abc'} = 7 if (! $i); foreach my $key (keys %hash) { print "the key is $key and val is $hash{$key}\n" }` [download] Im so sick of my Signature...	[reply] [d/l]
Re: Initializing a hash using conditions by rir (Vicar) on Feb 03, 2005 at 14:34 UTC
I prefer moving the conditional out of the initial assignment, but that is a thoughtless prejudice of habit and society. I recommend the inline ternary solutions that you've recieved. I post because those solve your immediate problem but don't address the fundamental problem with your code: `%hash = ( ( 'abc' => 7) if ( ! $i), );` [download] The primary problem is that you are placing a statement where an expression is expected. A general solution to this problem is to use a `do` `BLOCK` that ends with the value you want. `%hash = ( do{ if ( $i) { abc => 7 } else { } }, );` [download] Be well, rir	[reply] [d/l] [select]
Re: Initializing a hash using conditions by punkish (Priest) on Feb 03, 2005 at 12:29 UTC
for questions that start with... I was wondering if I can... the answer is... why not just try it and see if you can. If it is wrong, Perl will complain, especially if you have used `-w` and `strict`. The above won't compile. However, if you change it ever so slightly, it will. Keep in mind that the right side of => or any element in an array, for that matter, can be the result of an expression. Convert your if... else... statement into the ternary form and it will work... `%hash = ( 'abc' => !$i ? 7 : '', 'hk' => 5, 'jk' => 6 ); # a ternary expression is $var = condition ? if_true : if_false` [download] Good luck.	[reply] [d/l] [select]
Re: Initializing a hash using conditions by stvn_skuo (Initiate) on Feb 04, 2005 at 07:07 UTC
Use the repetition operator: `my $i = 1; my %hash = ( ('abc' => 7) x (! $i), 'hk' => 5, 'jk' => 6 ); my %other_hash = ( ('abc' => 7) x (!! $i), 'hk' => 5, 'jk' => 6 );` [download]	[reply] [d/l]