Array merge and combine in PHP - Step-by-Step Execution

Concept Flow - Array merge and combine

Start with two arrays

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Choose operation: merge or combine

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Merge: append values

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Result: combined values, keys reindexed

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Combine: keys from first, values from second

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Result: new array with keys and values paired

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Use or display result

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End

Start with two arrays, then either merge by appending values or combine by pairing keys and values, then use the result.

Execution Sample

PHP

<?php
$array1 = ["a", "b"];
$array2 = ["c", "d"];
$merged = array_merge($array1, $array2);
$combined = array_combine($array1, $array2);
print_r($merged);
print_r($combined);
?>

This code merges two arrays by appending and combines them by pairing keys from the first with values from the second.

Execution Table

Step	Operation	Input Arrays	Result	Notes
1	Start	["a", "b"] and ["c", "d"]	N/A	Initial arrays
2	array_merge	["a", "b"], ["c", "d"]	["a", "b", "c", "d"]	Values appended, keys reindexed
3	array_combine	["a", "b"], ["c", "d"]	["a" => "c", "b" => "d"]	Keys from first array, values from second
4	End	N/A	Merged and combined arrays ready	Execution complete

💡 All operations complete, arrays merged and combined successfully

Variable Tracker

Variable	Start	After Merge	After Combine	Final
$array1	["a", "b"]	["a", "b"]	["a", "b"]	["a", "b"]
$array2	["c", "d"]	["c", "d"]	["c", "d"]	["c", "d"]
$merged	N/A	["a", "b", "c", "d"]	["a", "b", "c", "d"]	["a", "b", "c", "d"]
$combined	N/A	N/A	["a" => "c", "b" => "d"]	["a" => "c", "b" => "d"]

Key Moments - 3 Insights

Why does array_merge reindex keys instead of keeping original keys?

array_merge appends values and assigns new numeric keys starting from 0, as shown in step 2 of the execution_table, so keys are reindexed.

What happens if the first array has duplicate values when using array_combine?

array_combine uses the first array as keys, so duplicate values in the first array result in duplicate keys, but the last value overwrites previous ones for that key; no error is thrown.

Can array_combine be used if arrays have different lengths?

No, array_combine requires both arrays to have the same number of elements, otherwise it will produce a warning or error, as implied by the need for pairing in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $merged after step 2?

A ["a" => "c", "b" => "d"]

B ["a", "b", "c", "d"]

C ["a", "b"]

D ["c", "d"]

💡 Hint

Check the 'Result' column for step 2 in the execution_table.

At which step does the array_combine operation occur?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Operation' column in the execution_table for array_combine.

If $array1 had 3 elements but $array2 had 2, what would happen to array_combine?

A It would ignore extra elements in $array1

B It would combine only first 2 pairs

C It would produce an error or warning

D It would merge arrays instead

💡 Hint

Recall from key_moments that array_combine requires arrays of equal length.

Concept Snapshot

array_merge($a1, $a2): appends values, reindexes keys
array_combine($a1, $a2): pairs keys from $a1 with values from $a2
Both require arrays as input
array_combine needs arrays of equal length
Use merge to join values, combine to create key-value pairs

Full Transcript

This visual execution trace shows how PHP's array_merge and array_combine functions work. Starting with two arrays, array_merge appends the values of the second array to the first and reindexes keys starting from zero. Array_combine pairs keys from the first array with values from the second array, creating a new associative array. The execution table traces each step, showing inputs and results. Key moments clarify common confusions like why keys are reindexed in merge and the requirement for equal array lengths in combine. The visual quiz tests understanding of these steps and behaviors. The concept snapshot summarizes the syntax and key rules for these functions.