FAQ 4.49 How do I process/modify each element of an array?

Discussion in 'Perl Misc' started by PerlFAQ Server, Mar 24, 2011.

  1. This is an excerpt from the latest version perlfaq4.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    4.49: How do I process/modify each element of an array?

    Use "for"/"foreach":

    for (@lines) {
    s/foo/bar/; # change that word
    tr/XZ/ZX/; # swap those letters
    }

    Here's another; let's compute spherical volumes:

    for (@volumes = @radii) { # @volumes has changed parts
    $_ **= 3;
    $_ *= (4/3) * 3.14159; # this will be constant folded
    }

    which can also be done with "map()" which is made to transform one list
    into another:

    @volumes = map {$_ ** 3 * (4/3) * 3.14159} @radii;

    If you want to do the same thing to modify the values of the hash, you
    can use the "values" function. As of Perl 5.6 the values are not copied,
    so if you modify $orbit (in this case), you modify the value.

    for $orbit ( values %orbits ) {
    ($orbit **= 3) *= (4/3) * 3.14159;
    }

    Prior to perl 5.6 "values" returned copies of the values, so older perl
    code often contains constructions such as @orbits{keys %orbits} instead
    of "values %orbits" where the hash is to be modified.



    --------------------------------------------------------------------

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    PerlFAQ Server, Mar 24, 2011
    #1
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