Case insensitive hash key existance

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

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Re: Case insensitive hash key existance by Your Mother (Archbishop) on Nov 22, 2017 at 15:44 UTC
Probably `$data{fc $str}` (in every instance of using the hash key) if your Perl is new enough. `$data{lc $str}` otherwise. The later may come with surprises if you deal with "wide characters."	[reply] [d/l] [select]
Re: Case insensitive hash key existance by haukex (Archbishop) on Nov 22, 2017 at 15:47 UTC
Google / Super Search is your friend, just a selection: Case insensitivity in a hash... Futile effort? Hash Keys case independent Not case sensitive hash? On creating hash whose keys aren't case-sensitive case-insensitive hash keys The only thing I have to add at the moment is that as of Perl 5.16 in addition to lc there is fc which might be useful if you have Unicode data. (Update: Didn't see Your Mother's post before posting.)	[reply]
Re: Case insensitive hash key existance by kennethk (Abbot) on Nov 22, 2017 at 16:00 UTC
If you have an existing hash (thus fc is not an option), you can grep the key set against a case-insensitive regular expression: `if(grep /^\Q$str\E$/i, keys %data) { # case-insensitive exists` [download] This solves an immediate problem, though making sure your keys were well-formed in the first place would probably be cleaner. #11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.	[reply] [d/l]
Re^2: Case insensitive hash key existance by Your Mother (Archbishop) on Nov 22, 2017 at 16:51 UTC
:P `if ( grep fc $str eq fc $_, keys %data ) { # case-insensitive exists` [download] Or to "fix" the data- `$data{fc$_} = delete $data{$_} for keys %data;` [download] As this example should make clear, and haukex's links explained, the entire operation is probably a bad idea as it is destructive (or at least has the appearance of being so if the plain folding is done without deleting.	[reply] [d/l] [select]
Re^2: Case insensitive hash key existance by merrymonk (Hermit) on Nov 22, 2017 at 16:31 UTC
Thanks for all the replies. I take the point about well formed data for keys and normally I would not want to do such a thing. However, there are reasons why it is OK in this case. The grep suggestion does just what I want.	[reply]
Re^3: Case insensitive hash key existance by ikegami (Patriarch) on Nov 22, 2017 at 17:09 UTC
Be warned of the massive performance hit. It replaces an O(1) lookup with than O(N) lookup. That's not good, but it's not so bad ...except that this is likely used in another another loop. Then that O(N) or O(N^2) loop because O(N^2) or O(N^3), and things start to crawl.	[reply]
Re: Case insensitive hash key existance by Anonymous Monk on Nov 22, 2017 at 15:57 UTC
Use a second hash to store the uppercased version of the original key, then store the data using that uppercased string. Q.E.D.	[reply]
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