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Your original code with strict and warnings:

use strict; use warnings; sub twice { 2 * $_[0] } my @a = map twice, 1..3; print "@a\n";
gives the warning "Use of uninitialized value $_[0] in multiplication (*) at map1.pl line 3".

This is how it should be written:

use strict; use warnings; sub twice { 2 * $_[0] } my @a = map twice($_), 1..3; print "@a\n";
which produces 2 4 6 as expected.

BTW, Conway, in Perl Best Practices, chapter 8, recommends always using the block form of map, not the expression form that you are using. The expression form might be faster than the block form though (if that matters, you should benchmark it).


In reply to Re^3: Problems with map(function, array) by eyepopslikeamosquito
in thread Problems with map(function, array) by Redei

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    [Cosmic37]: greetings earthlings please can someone improve my pathetic perl knowledge
    [Cosmic37]: I have 2 files each with datetime and other data in unknown order and I want to find rows from both files matching by datetime and output them combined/ concatenated
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    [Corion]: Cosmic37: Ah, see perlfaq4, about How do I compute the intersection of two arrays
    [Cosmic37]: I am out of practice; I use Perl for scientific programming for number crunching
    [Corion]: Cosmic37: Basically, you read one file into a hash, keyed by your key, and then match the lines from the second file to that hash

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