php - how to merge 2d array that have different no of element for each array

$out = array();
for ($i=0; $i<count($arr1); $i++){
    $out[] = array_values(array_unique(array_merge($arr1[$i], $arr2[$i])));
}
var_dump($out);

Output:

Array
(
    [0] => Array
        (
            [0] => 25/2/2013
            [1] => 8.45 a.m
            [2] => 9.98
            [3] => 1.23
            [4] => 6.1
        )

    [1] => Array
        (
            [0] => 25/2/2013
            [1] => 8.46 a.m
            [2] => 9.02
            [3] => 1.75
        )

)

It depends a lot on what your actual goal is. For instance, from your example, it seems that you want to use the date [index 0] (and possibly the time [index 1]) as a "primary key" of sorts, to control how data is merged.

There is no suitable function for this built in to PHP (as you've noticed, array_merge_recursive doesn't do what you want): you'll have to roll your own. There are a lot of "edge cases" to consider.

<?php
/**
 * recursively merges each item in $a1 and $a2 if their indexes [0] and [1] match;
 * appends the $a2 item instead if no matching item is found in $a1.
 *
 * @param  array  $a1 the first array to merge
 * @param  array  $a2 the second array to merge
 * @return array  the merged array
 */
function key_01_merge( array $a1,array $a2 ){
    // loop through each item in $a2
    foreach( $a2 as $a2_item ){
        // make sure it's an array with [0] and [1]
        if(
            ! is_array( $a2_item )
            || empty( $a2_item[0] )
            || empty( $a2_item[1] )
        ){
            // invalid; skip it
            break;
        }
        // compare it to each item in $a1; checking for matching "keys"
        foreach( $a1 as $a1_key => $a1_item ){
            if( 
                ! empty( $a1_item[0] )
                && ! empty( $a1_item[1] )
                && $a1_item[0] === $a2_item[0] 
                && $a1_item[1] === $a2_item[1] 
            ){
                // merge the two arrays
                // filter duplicate values
                // assign resulting array to the original index in $a1
                $a1[$a1_key] = array_unique( 
                    array_merge_recursive( $a1_item,$a2_item )
                );
                // set this item as "false" so it won't be appended to $a1
                $a2_item = false;
                // stop; continue with next item in $a2
                break;
            }
        }
        // if $a2_item was merged, it is now false;
        // otherwise, append it to the $a1 array
        if( $a2_item ){
            $a1[] = $a2_item;
        }
    }
    // return the $a1 array
    return $a1;
}

tested.

$a1 = [
    0 => [
        0 => '25/2/2013'
       ,1 => '8.45 a.m'
       ,2 => '9.98'
    ]
   ,1 => [
        0 => '25/2/2013'
       ,1 => '8.46 a.m'
       ,2 => '9.02'
    ]
];
$a2 = [   
    0 => [
        0 => '25/2/2013'
       ,1 => '8.45 a.m'
       ,2 => '1.23'
       ,3 => '6.1'
    ]
   ,1 => [
        0 => '25/2/2013'
       ,1 => '8.46 a.m'
       ,2 => '1.75'
       ,3 => '3.5'
    ]
];

var_dump( key_01_merge( $a1,$a2 ) );

outputs:

/*
array(2) {
  [0]=>
  array(5) {
    [0]=>
    string(9) "25/2/2013"
    [1]=>
    string(8) "8.45 a.m"
    [2]=>
    string(4) "9.98"
    [5]=>
    string(4) "1.23"
    [6]=>
    string(3) "6.1"
  }
  [1]=>
  array(5) {
    [0]=>
    string(9) "25/2/2013"
    [1]=>
    string(8) "8.46 a.m"
    [2]=>
    string(4) "9.02"
    [5]=>
    string(4) "1.75"
    [6]=>
    string(3) "3.5"
  }
}
*/

use array_merge_recursive example

$array = array_merge_recursive($array1, $array2);
 var_dump($array);