Removing duplicate items from an array Post: 303007455

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Top Forums Shell Programming and Scripting Removing duplicate items from an array Post 303007455 by Don Cragun on Thursday 16th of November 2017 09:20:55 PM

11-16-2017

Registered User

Quote:

Originally Posted by mukulverma2408

Hi Don,

Thanks for your reply, the script is now working perfectly.

Can you please help to explain below part, the script seems to be working fine without decreasing the counter as well.

Code:

((j--))

The script is decreasing the counters.

After removing an element from the array of n items, the arithmetic command ((n--)) decreases the value of n. Note that n-1 is also the upper limit on the outer loop (indexed by i) and n is the upper limit on the inner loop (indexed by j).

When we remove an element from the array (i.e. remove ${array[$j]} by moving higher elements of the array down one position), the ((j--)) forces the next iteration of the inner loop to look at the same element (after moving down higher elements). Without the ((j--)) the first element that was moved down won't be examined to see if it is also a duplicate of the element indexed by the outer loop.

P.S.: Note also that your script compared every element of the array to every element of the array (skipping the cases where it was comparing an item to itself). My script compares element 1 in the array to elements 2 through n, then compares element 2 to elements 3 through n, and so on until it compares element n-1 to element n on the last iteration through the nested loops. Doing it this way eliminates the need to check for comparing an element to itself and gets rid of the duplicated comparisons with pairs of elements that have already been compared.

Last edited by Don Cragun; 11-16-2017 at 10:37 PM.. Reason: Add postscript.

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LEARN ABOUT PHP

collator_sort

COLLATOR_SORT(3)							 1							  COLLATOR_SORT(3)

Collator::sort - Sort array using specified collator

	Object oriented style

SYNOPSIS

       public bool Collator::sort (array  &$arr, [int  $sort_flag])

DESCRIPTION

	Procedural style
       bool collator_sort (Collator  $coll, array  &$arr, [int	$sort_flag])

       This function sorts an array according to current locale rules.

	Equivalent to standard PHP sort(3) .

PARAMETERS

	      o $coll
		-Collator object.

	      o $arr
		- Array of strings to sort.

	      o $sort_flag
		- Optional sorting type, one of the following:

		     o Collator::SORT_REGULAR - compare items normally (don't change types)

		     o Collator::SORT_NUMERIC - compare items numerically

		     o Collator::SORT_STRING - compare items as strings

	       Default sorting type is Collator::SORT_REGULAR. It is also used if an invalid $sort_flag value has been specified.

RETURN VALUES

	Returns TRUE on success or FALSE on failure.

EXAMPLES

       Example #1

	      collator_sort(3) example

	      <?php
	      $coll = collator_create( 'en_US' );
	      $arr  = array( 'at', 'as', 'as' );

	      var_export( $arr );
	      collator_sort( $coll, $arr );
	      var_export( $arr );
	      ?>

	      The above example will output:

	      array (
		0 => 'at',
		1 => 'as',
		2 => 'as',
	      )array (
		0 => 'as',
		1 => 'as',
		2 => 'at',
	      )

SEE ALSO

       Collator constants, collator_asort(3), collator_sort_with_sort_keys(3).

PHP Documentation Group 													  COLLATOR_SORT(3)