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

seekableiterator

SEEKABLEITERATOR(3)							 1						       SEEKABLEITERATOR(3)

The SeekableIterator interface

INTRODUCTION

	The Seekable iterator.

INTERFACE SYNOPSIS

       SeekableIterator

       SeekableIteratorextends
       Iterator

       Methods

       o abstractpublic void SeekableIterator::seek (int  $position)

       Inherited methods

       o abstractpublic mixed Iterator::current (void  )

       o abstractpublic scalar Iterator::key (void  )

       o abstractpublic void Iterator::next (void  )

       o abstractpublic void Iterator::rewind (void  )

       o abstractpublic boolean Iterator::valid (void  )

       Example #1

	      Basic usage

	       This example demonstrates creating a custom SeekableIterator, seeking to a position and handling an invalid position.

	      <?php
	      class MySeekableIterator implements SeekableIterator {

		  private $position;

		  private $array = array(
		      "first element",
		      "second element",
		      "third element",
		      "fourth element"
		  );

		  /* Method required for SeekableIterator interface */

		  public function seek($position) {
		    if (!isset($this->array[$position])) {
			throw new OutOfBoundsException("invalid seek position ($position)");
		    }

		    $this->position = $position;
		  }

		  /* Methods required for Iterator interface */

		  public function rewind() {
		      $this->position = 0;
		  }

		  public function current() {
		      return $this->array[$this->position];
		  }

		  public function key() {
		      return $this->position;
		  }

		  public function next() {
		      ++$this->position;
		  }

		  public function valid() {
		      return isset($this->array[$this->position]);
		  }
	      }

	      try {

		  $it = new MySeekableIterator;
		  echo $it->current(), "
";

		  $it->seek(2);
		  echo $it->current(), "
";

		  $it->seek(1);
		  echo $it->current(), "
";

		  $it->seek(10);

	      } catch (OutOfBoundsException $e) {
		  echo $e->getMessage();
	      }
	      ?>

	      The above example will output something similar to:

	      first element
	      third element
	      second element
	      invalid seek position(10)

PHP Documentation Group 												       SEEKABLEITERATOR(3)

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