How to sort in perl on the basis of one field.

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

Hi All, I have the below data as the elements of an array (lets say @array).

field1,fieldA,fileda     (1st element)
field2,fieldB,filedb           (2nd element & on)
field3,fieldC,filedc
[download]

where all fields are numeric values. now I need to join these elements in one scalar value ($all_data) but only after they are sorted in descending order on the basis of second field (ie fieldA, fieldB). Any one pls could help me in this...Pls let me knoe if you need more info. on that...thanks a lot

Comment on How to sort in perl on the basis of one field. Download Code

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Re: How to sort in perl on the basis of one field. by bigj (Monk) on Jul 29, 2014 at 05:54 UTC
What have you tried so far? I won't make your homework, but I might give you some hints. To sort a list/array in perl, we have the sort function, to make it descending numericaly, usually, we'll have something like `my @sorted_array = sort {$b <=> $a} @array` or `my @sorted_array = reverse sort {$a <=> $b} @array`. To join something, we'll work with join usually :-) or for more flexible transformations with map. To get some fields seperated by a delimiter, we'd probably use split or in a more complex situation maybe a specialised module like Text::CSV for a CSV-file like your one looks also. So overall, you'll probably just translate your description into some perlish code 1:1 with the above built in ops/functions/modules. Greetings, Janek Schleicher	[reply] [d/l] [select]
Re: How to sort in perl on the basis of one field. by Laurent_R (Canon) on Jul 29, 2014 at 06:15 UTC
First split your array elements in order to get an array of arrays (AoA). Something like this (untested) `my @AoA = [split /[,\s]+/, $_] for @array;` [download] Then sort the AoA according to the second element. For a numerical sort, something like this (also untested): `@AoA = sort { $b->[1] <=> $a->[1] } @AoH;` [download] Then you can join the elements of the inner arrays using join or map, I'll leave it to you (you don't give enough details). The whole thing could be done in one single pipeline step, but since you appear to be a beginner, it is probably better to make in in 3 steps as explained above.	[reply] [d/l] [select]
Re: How to sort in perl on the basis of one field. by 2teez (Vicar) on Jul 29, 2014 at 07:07 UTC
Hi Aukur kuls, If I may add my voice to that of others, that what you seek can be done in a single "breath" with what is called popularly known as Schwartzian Transform. Using a modified version of what you posted one can do: `use warnings; use strict; print map { $_->[0] } sort { $b->[1] <=> $a->[1] } map { [ $_, ( split /[,\s\D]+/, $_ )[2] ] } <DATA>; __DATA__ field15,field78,filed0 field90,field12,filed23 field3,field55,filed67` [download] If you tell me, I'll forget. If you show me, I'll remember. if you involve me, I'll understand. --- Author unknown to me	[reply] [d/l]
Re: How to sort in perl on the basis of one field. by Anonymous Monk on Jul 29, 2014 at 07:10 UTC
Split columns according header delimiter, http://learn.perl.org/faq/perlfaq4.html#How-do-I-sort-an-array-by-anything-, http://perldoc.perl.org/perlfaq4.html#How-do-I-sort-an-array-by-%28anything%29%3f Understanding the Schwartzian transform., Re: Sorting a HoH by values of the nested hashes, Path::Tiny	[reply]
Re: How to sort in perl on the basis of one field. by rovf (Priest) on Jul 29, 2014 at 05:52 UTC
How are they joined? I guess you use some separator to join then. In this case, you can use (in your sort function) a regular expression to extract the second field, and sort on it. -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l]


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