how to put element of an array to first position.


 
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# 1  
Old 06-17-2010
how to put element of an array to first position.

hi,

I have a array like

my $array = ( "apple","ball","cat","dog","elephant");

how to push some element in the array to the first position.
for example my final array should be

elephant apple ball cat dog
# 2  
Old 06-17-2010
homework?

perldoc
push, pop, shift, unshift
# 3  
Old 06-17-2010
I assume, from the "my" keyword, you're using perl

One way to do this would be like this

unshift(@array,pop(@array));
# 4  
Old 06-18-2010
i tried this one to shift the element elephant to first position , but its not working, $_ is showing nothing here

if(grep $_ =~ m/elephant/, @array) {

unshift(@array, $_);
}

after moving the required element to the first position i want to remove that element from previous position.any help is appreciated.
# 5  
Old 06-18-2010
If you want to check the value, you'll need to do something like this:

Code:
#! /usr/bin/perl -w

use Data::Dumper;

my @array = ("apple","ball","cat","dog","elephant");

$_ = pop(@array);

if(m/elephant/) {
unshift(@array, $_);
}

print Dumper(@array);

Notice that the m// is implicitly working on the $_ variable.
# 6  
Old 06-26-2010
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
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