How to merge the first index of an array with the first index of second array?

The task is to merge the first index of an array with the first index of another array. Suppose, an array is array1 = {a, b, c} and another array is array2 = {c, d, e} if we perform the task on these arrays then the output will be 

result array
    { 
    [0]=> array(2) 
        { 
        [0]=> string(1) "a" 
        [1]=> string(1) "c" 
        } 
    [1]=> array(2) 
        { 
        [0]=> string(1) "b" 
        [1]=> string(1) "d" 
        } 
    [2]=> array(2) 
            { 
            [0]=> string(1) "c" 
            [1]=> string(1) "e" 
            } 
    }

Most people think array_merge() function can resolve the above requirement the following code shows how this isn't the way to achieve it: 

Example 1: Using the array_merge() function will give you the desired result.

<?php
    $array1=array("a","b","c");
    $array2=array("c","d","e");
    $result=array_merge($array1,$array2);
    var_dump($result);
?>

Output: 

array(6) { [0]=> string(1) "a" 
           [1]=> string(1) "b" 
           [2]=> string(1) "c" 
           [3]=> string(1) "c" 
           [4]=> string(1) "d" 
           [5]=> string(1) "e" 
         }

In order to combine the two arrays by indices, we have to loop through them and merge as we go. Such that the first index of the first and second array together form the first index of the resultant array.

Example 2: Program to merge 2 simple arrays 

<?php
    $array1=array("a","b","c");
    $array2=array("c","d","e");
    $result=array();
    foreach($array1 as $key=>$value ){
      $val=$array2[$key];
      $result[$key]=array($value,$val);
    }

    var_dump($result);
?>

Output: 

array(3) { 
    [0]=> array(2) 
        { 
        [0]=> string(1) "a" 
        [1]=> string(1) "c" 
        } 
    [1]=> array(2) 
        { 
        [0]=> string(1) "b" 
        [1]=> string(1) "d" 
        } 
    [2]=> array(2) 
            { 
            [0]=> string(1) "c" 
            [1]=> string(1) "e" 
            } 
    }

Example 3: Program to merge 2 complex arrays 

<?php
    $array1=array(array("a","b"),array("c","d"));
    $array2=array(array("z","y"),array("x","w"));
    $result=array();
    foreach($array1 as $key=>$value ){
      $val=$array2[$key];
      $result[$key]=array($value,$val);
    }

    var_dump($result);
?>

Output: 

array(2) { 
    [0]=> array(2) 
        { 
        [0]=> array(2) 
            { 
            [0]=> string(1) "a" 
            [1]=> string(1) "b" 
            } 
        [1]=> array(2) 
            { 
            [0]=> string(1) "z" 
            [1]=> string(1) "y" 
            } 
        } 
    [1]=> array(2) 
        {
        [0]=> array(2) 
            { 
            [0]=> string(1) "c" 
            [1]=> string(1) "d" 
            } 
        [1]=> array(2) 
            { 
            [0]=> string(1) "x" 
            [1]=> string(1) "w" 
            } 
        } 
    }

Using Array Concatenation

To merge the first index of one array with the first index of another in PHP, use array concatenation: $mergedArray = [$array1[0], $array2[0]]. This directly creates a new array with the desired elements.

Example: This example shows the implementation of the above-mentioned approach.

<?php
// First array
$array1 = ['apple', 'banana', 'cherry'];

// Second array
$array2 = ['orange', 'grape', 'melon'];

// Create a new array by directly concatenating the first elements
$mergedArray = [$array1[0], $array2[0]];

// Print the merged array
print_r($mergedArray);
?>

Array
(
    [0] => apple
    [1] => orange
)

Using the array_reduce Function

Using array_reduce merges arrays by iterating through keys, combining corresponding elements into a new array. This function builds the merged array by applying a callback function that appends pairs of elements from both arrays into the result, ensuring indices are aligned correctly.

Example

<?php
$array1 = ["a", "b", "c"];
$array2 = ["c", "d", "e"];

$mergedArray = array_reduce(
    array_keys($array1),
    function ($carry, $key) use ($array1, $array2) {
        if (isset($array2[$key])) {
            $carry[] = [$array1[$key], $array2[$key]];
        }
        return $carry;
    },
    []
);

print_r($mergedArray);
?>

Array
(
    [0] => Array
        (
            [0] => a
            [1] => c
        )

    [1] => Array
        (
            [0] => b
            [1] => d
        )

    [2] => Array
        (
     ...

Using array_replace() Function

The array_replace() function in PHP replaces values of the first array with values from subsequent arrays using their keys. To merge the first index of two arrays, you can use array_replace() by extracting and replacing the desired index values.

Example

<?php
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];

$array1[0] = $array2[0]; // Replace first index
print_r($array1); // Output: [4, 2, 3]
?>

Array
(
    [0] => 4
    [1] => 2
    [2] => 3
)