Array unique and flip in PHP - Step-by-Step Execution

Concept Flow - Array unique and flip

Start with array

↓

Apply array_unique

↓

Remove duplicate values

↓

Apply array_flip

↓

Swap keys and values

↓

Result: flipped unique array

Start with an array, remove duplicates with array_unique, then swap keys and values using array_flip.

Execution Sample

PHP

<?php
$arr = ["a", "b", "a", "c"];
$unique = array_unique($arr);
$flipped = array_flip($unique);
print_r($flipped);
?>

This code removes duplicates from the array and then flips keys and values.

Execution Table

Step	Action	Array State	Output/Result
1	Start with array	["a", "b", "a", "c"]	Initial array
2	Apply array_unique	[0 => "a", 1 => "b", 3 => "c"]	Duplicates removed, keys preserved
3	Apply array_flip	["a" => 0, "b" => 1, "c" => 3]	Keys and values swapped
4	Print result	Same as step 3	Array printed with flipped keys and values

💡 All duplicates removed and keys/values flipped, process complete.

Variable Tracker

Variable	Start	After array_unique	After array_flip	Final
$arr	["a", "b", "a", "c"]	["a", "b", "a", "c"]	["a", "b", "a", "c"]	["a", "b", "a", "c"]
$unique	N/A	[0 => "a", 1 => "b", 3 => "c"]	[0 => "a", 1 => "b", 3 => "c"]	[0 => "a", 1 => "b", 3 => "c"]
$flipped	N/A	N/A	["a" => 0, "b" => 1, "c" => 3]	["a" => 0, "b" => 1, "c" => 3]

Key Moments - 2 Insights

Why does array_unique keep the original keys instead of reindexing?

array_unique preserves the original keys to keep track of the first occurrence of each unique value, as shown in step 2 of the execution_table where keys 0,1,3 remain.

What happens if array_flip is used on an array with duplicate values?

array_flip will overwrite keys for duplicate values because keys must be unique. Using array_unique first avoids this issue, as shown in step 3 where flipped keys are unique.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the key for value "c" after array_unique?

A 3

B 2

C 1

D 0

💡 Hint

Check the 'Array State' column at step 2 in the execution_table.

At which step does the array keys and values get swapped?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for the action 'Apply array_flip' in the execution_table.

If the original array had no duplicates, how would the array_unique step change?

A It would reindex the keys

B It would remove some elements

C It would keep the array unchanged

D It would flip keys and values

💡 Hint

Refer to the variable_tracker for $unique after array_unique.

Concept Snapshot

array_unique(array) removes duplicate values but keeps original keys.
array_flip(array) swaps keys and values.
Use array_unique before array_flip to avoid key conflicts.
Resulting array has unique values as keys and original keys as values.

Full Transcript

We start with an array that may have duplicate values. First, we use array_unique to remove duplicates but keep the original keys. Then, we apply array_flip to swap keys and values. This process ensures the flipped array has unique keys. The execution table shows each step's array state and output. Key moments clarify why keys are preserved and why duplicates must be removed before flipping. The visual quiz tests understanding of keys after unique and when flipping happens. The snapshot summarizes the key points for quick recall.