how to put element of an array to first position. Post: 302432748

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Top Forums Programming how to put element of an array to first position. Post 302432748 by drl on Saturday 26th of June 2010 12:32:58 PM

06-26-2010

Registered User

Hi.

I was reading in Perl Best Practices - O'Reilly Media , and ran across a function first_index that resides in a recommended module, List::MoreUtils. Here are a few possibly-related ideas using such a function to identify an entry, then remove it to one end of the other of an array with the help of in-built functions splice. push, and unshift:

Code:

#!/usr/bin/env perl

# @(#) p1	Demonstrate list entry identification, movement.

use warnings;
use strict;
use List::MoreUtils qw( first_index );

my ( $debug, @a, @original, $t1, $t2 );
$debug = 1;
$debug = 0;

my ($want) = "cat";
@original = qw/ pig goat catastrophe cat dog turkey deer /;

@a = @original;

print "\n";
print " For simple string equality, \"cat\", constant, then variable:\n";
print "\n";
print " Constant, just to see a simple example:\n";
print "a (original   ) is :@a:\n";

$t1 = first_index { $_ eq "cat" } @a;
print $t1, "\n" if $debug;

$t2 = splice( @a, $t1, 1 );
print $t2, "\n" if $debug;

unshift @a, $t2;
print "a (for unshift) is :@a:\n";

print "\n";
print " Now with variables, a more likely situation:\n";
@a = @original;
print "a (original   ) is :@a:\n";

$t1 = first_index { $_ eq $want } @a;
print $t1, "\n" if $debug;

$t2 = splice( @a, $t1, 1 );
print $t2, "\n" if $debug;

unshift @a, $t2;
print "a (for unshift) is :@a:\n";

print "\n";
@a = @original;
print "a (original   ) is :@a:\n";

$t1 = first_index { $_ eq $want } @a;
print $t1, "\n" if $debug;

$t2 = splice( @a, $t1, 1 );
print $t2, "\n" if $debug;

push @a, $t2;
print "a (for push   ) is :@a:\n";

print "\n";
@a = @original;
print "a (original   ) is :@a:\n";
unshift @a, splice( @a, ( first_index { $_ eq $want } @a ), 1 );

print "a (single line) is :@a:\n";

@a = @original;

print "\n";
print " For string match regular expression, /$want/:\n";
print "\n";
print "a (original   ) is :@a:\n";

$t1 = first_index { $_ =~ m/$want/ } @a;
print $t1, "\n" if $debug;

$t2 = splice( @a, $t1, 1 );
print $t2, "\n" if $debug;

unshift @a, $t2;
print "a (for unshift) is :@a:\n";

exit(0);

producing:

Code:

% ./p1

 For simple string equality, "cat", constant, then variable:

 Constant, just to see a simple example:
a (original   ) is :pig goat catastrophe cat dog turkey deer:
a (for unshift) is :cat pig goat catastrophe dog turkey deer:

 Now with variables, a more likely situation:
a (original   ) is :pig goat catastrophe cat dog turkey deer:
a (for unshift) is :cat pig goat catastrophe dog turkey deer:

a (original   ) is :pig goat catastrophe cat dog turkey deer:
a (for push   ) is :pig goat catastrophe dog turkey deer cat:

a (original   ) is :pig goat catastrophe cat dog turkey deer:
a (single line) is :cat pig goat catastrophe dog turkey deer:

 For string match regular expression, /cat/:

a (original   ) is :pig goat catastrophe cat dog turkey deer:
a (for unshift) is :catastrophe pig goat cat dog turkey deer:

cheers, drl

drl

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LEARN ABOUT PHP

array_walk_recursive

ARRAY_WALK_RECURSIVE(3) 						 1						   ARRAY_WALK_RECURSIVE(3)

array_walk_recursive - Apply a user function recursively to every member of an array

SYNOPSIS

       bool array_walk_recursive NULL (array  &$array, callable  $callback, [mixed  $userdata])

DESCRIPTION

	Applies the user-defined $callback function to each element of the $array. This function will recurse into deeper arrays.

PARAMETERS

	      o $array
		- The input array.

	      o $callback
		- Typically, $callback takes on two parameters. The $array parameter's value being the first, and the key/index second.

	      Note

		      If  $callback  needs to be working with the actual values of the array, specify the first parameter of $callback as a refer-
		     ence. Then, any changes made to those elements will be made in the original array itself.

	      o $userdata
		- If the optional $userdata parameter is supplied, it will be passed as the third parameter to the $callback.

RETURN VALUES

	Returns TRUE on success or FALSE on failure.

EXAMPLES

       Example #1

	      array_walk_recursive(3) example

	      <?php
	      $sweet = array('a' => 'apple', 'b' => 'banana');
	      $fruits = array('sweet' => $sweet, 'sour' => 'lemon');

	      function test_print($item, $key)
	      {
		  echo "$key holds $item
";
	      }

	      array_walk_recursive($fruits, 'test_print');
	      ?>

	      The above example will output:

	      a holds apple
	      b holds banana
	      sour holds lemon

	       You may notice that the key ' sweet' is never displayed. Any key that holds an array will not be passed to the function.

SEE ALSO

       array_walk(3), information about the callback type.

PHP Documentation Group 												   ARRAY_WALK_RECURSIVE(3)

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