hash to count occurences

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

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Re: hash to count occurences by LanX (Saint) on Oct 25, 2013 at 17:24 UTC
open file, <iterate over lines>, split column-elements from each line into array `@elements` increment hash `%count`per element like in `$count{$element[11]}++` see also How do I post a question effectively? and How (Not) To Ask A Question Cheers Rolf ( addicted to the Perl Programming Language)	[reply] [d/l] [select]
Re^2: hash to count occurences by gayagrad (Initiate) on Oct 25, 2013 at 19:32 UTC
Thank you	[reply]
Re: hash to count occurences by davido (Cardinal) on Oct 25, 2013 at 17:37 UTC
The shortest path (we all love short paths) to getting a good answer to this question would be to follow-up in this thread with a brief example of the input data that includes examples of any possible quirks the data might exhibit. Also post 20 lines or less of what code you've already written to get started in the project. Then ask a specific question about the portion of the project where you're stuck. Having read perlintro first will enable you to better understand the advice that follows. perlintro should take about 30 minutes to get through, and it's a reasonable expectation on our part that you become familiar with it first. Dave	[reply]
Re: hash to count occurences by Lennotoecom (Pilgrim) on Oct 25, 2013 at 22:14 UTC
Actual example: `foreach (split /\s/, <DATA>){ $hash{$_}++; } foreach $key (sort keys %hash){ print "$key $hash{$key}\n"; } __DATA__ SINE LINE LINE LINE SINE Alu Alu SINE` [download] output will be `Alu 2 LINE 3 SINE 3` [download] that __DATA__ thing at the end of the script is kind of an emulation of a real file inside script - handy. In the first line we take a single line from the <DATA> and split it by spaces (\s) into $_ variable one by one. Then we put into hash values which are sent by foreach and increment them if they are exist and if not, they are automatically created and incremented right after creation. And the second foreach cycle print keys and values from the newly created hash.	[reply] [d/l] [select]
Re: hash to count occurences by Anonymous Monk on Oct 25, 2013 at 17:27 UTC
Probably won't help :) perlintro DBD::CSV, Modern Perl a loose description of how experienced and effective Perl 5 programmers work....You can learn this too. Read more... (3 kB) DataExtract::FixedWidth / Parse::FixedRecord / Text::FixedWidth Learn Perl in about 2 hours 30 minutes	[reply] [d/l]
Re: hash to count occurences by Anonymous Monk on Oct 25, 2013 at 18:14 UTC
The "secret sauce" is in the line such as `$myhash->{'mykey'}++`. Welcome to what Perl calls "auto-vivification." If a hash-entry does not yet exist, it will be created with the initial value of 1. If it does exist, it will be incremented. So you can write this one statement to "do what you want." After looping through all the data, iterate through the `keys` in the hash and look for values greater than 15.	[reply]
Re^2: hash to count occurences by LanX (Saint) on Oct 25, 2013 at 19:42 UTC
almost > If a hash-entry does not yet exist, it will be created with the initial value of 1. the initial value is undef, when incremented undef is interpreted as 0. Cheers Rolf ( addicted to the Perl Programming Language)	[reply]