10-11-2002
reversing a list
Hi Everyone,
I am reading in a list of IDs from a file that is is chronological order. My current code in simplified form looks like this (ksh by the way)
IDS=`awk -F\| '{print $1}' inputfile.txt`
for i in $IDS
do
do various things with that ID
done
inputfile.txt looks like this:
1|stuff|more stuff|etc
2|stuff|more stuff|etc
3|stuff|more stuff|etc
.
.
.
10000|stuff|more stuff|etc
What I would like to do is start with the last ID (10000) and work towards the first ID (1). This is an oversimplified example. There are gaps between IDs, the may not be consecutive. I cannot do a while loop starting with i=10000 and decrement to 1 due to this. Any ideas how I could reverse the values in $IDS before the for loop? The input file can be manipulated prior to calling the script. I thought there was a command to invert a list but I can't remember what it is and can't find it ( I searched the forum + google + man -k)
Thanks,
Tony
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LEARN ABOUT DEBIAN
moosex::attributehelpers::methodprovider::list
MooseX::AttributeHelpers::MethodProvider::List(3pm) User Contributed Perl Documentation MooseX::AttributeHelpers::MethodProvider::List(3pm)
NAME
MooseX::AttributeHelpers::MethodProvider::List - method generator for MooseX::AttributeHelpers::Collection::List
SYNOPSIS
package Stuff;
use Moose;
use MooseX::AttributeHelpers;
has 'options' => (
metaclass => 'Collection::List',
is => 'rw',
isa => 'ArrayRef[Str]',
default => sub { [] },
auto_deref => 1,
provides => {
elements => 'all_options',
map => 'map_options',
grep => 'filter_options',
find => 'find_option',
first => 'first_option',
last => 'last_option',
get => 'get_option',
join => 'join_options',
count => 'count_options',
empty => 'do_i_have_options',
sort => 'sorted_options',
}
);
no Moose;
1;
DESCRIPTION
This is a role which provides the method generators for MooseX::AttributeHelpers::Collection::List.
METHODS
meta
PROVIDED METHODS
count
Returns the number of elements in the list.
$stuff = Stuff->new;
$stuff->options(["foo", "bar", "baz", "boo"]);
my $count = $stuff->count_options;
print "$count
"; # prints 4
empty
If the list is populated, returns true. Otherwise, returns false.
$stuff->do_i_have_options ? print "Good boy.
" : die "No options!
" ;
find
This method accepts a subroutine reference as its argument. That sub will receive each element of the list in turn. If it returns true
for an element, that element will be returned by the "find" method.
my $found = $stuff->find_option( sub { $_[0] =~ /^b/ } );
print "$found
"; # prints "bar"
grep
This method accepts a subroutine reference as its argument. This method returns every element for which that subroutine reference
returns a true value.
my @found = $stuff->filter_options( sub { $_[0] =~ /^b/ } );
print "@found
"; # prints "bar baz boo"
map This method accepts a subroutine reference as its argument. The subroutine will be executed for each element of the list. It is
expected to return a modified version of that element. The return value of the method is a list of the modified options.
my @mod_options = $stuff->map_options( sub { $_[0] . "-tag" } );
print "@mod_options
"; # prints "foo-tag bar-tag baz-tag boo-tag"
sort
Sorts and returns the elements of the list.
You can provide an optional subroutine reference to sort with (as you can with the core "sort" function). However, instead of using $a
and $b, you will need to use $_[0] and $_[1] instead.
# ascending ASCIIbetical
my @sorted = $stuff->sort_options();
# Descending alphabetical order
my @sorted_options = $stuff->sort_options( sub { lc $_[1] cmp lc $_[0] } );
print "@sorted_options
"; # prints "foo boo baz bar"
elements
Returns all of the elements of the list
my @option = $stuff->all_options;
print "@options
"; # prints "foo bar baz boo"
join
Joins every element of the list using the separator given as argument.
my $joined = $stuff->join_options( ':' );
print "$joined
"; # prints "foo:bar:baz:boo"
get Returns an element of the list by its index.
my $option = $stuff->get_option(1);
print "$option
"; # prints "bar"
first
Returns the first element of the list.
my $first = $stuff->first_option;
print "$first
"; # prints "foo"
last
Returns the last element of the list.
my $last = $stuff->last_option;
print "$last
"; # prints "boo"
BUGS
All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to
cpan-RT.
AUTHOR
Stevan Little <stevan@iinteractive.com>
COPYRIGHT AND LICENSE
Copyright 2007-2009 by Infinity Interactive, Inc.
<http://www.iinteractive.com>
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.10.1 2010-01-02 MooseX::AttributeHelpers::MethodProvider::List(3pm)