Accessing Values by Key

Part of the Fundamentals section of Coddy's PHP journey — lesson 42 of 71.

Now that you understand what associative arrays are, let's learn how to retrieve values from them. Just like indexed arrays use numeric positions, associative arrays use keys inside square brackets.

<?php
$person = [
    "name" => "Alice",
    "age" => 25,
    "city" => "Paris"
];

echo $person["name"]; // Alice
echo $person["age"];  // 25
?>

The syntax is $array["key"]—place the key as a string inside the brackets, and PHP returns the associated value. This is much more readable than remembering that the name is at index 0.

You can also store the retrieved value in a variable for later use:

<?php
$product = [
    "title" => "Laptop",
    "price" => 999
];

$itemName = $product["title"];
echo $itemName; // Laptop
?>

The key must match exactly—including capitalization. Using "Name" instead of "name" would cause an error since PHP treats them as different keys.

Sometimes data arrives as a JSON string rather than a PHP array. JSON (JavaScript Object Notation) is a common text format for representing structured data. PHP's built-in json_decode() function converts a JSON string into a PHP value. When you pass true as the second argument, it returns an associative array instead of an object, so you can access values with the familiar $array["key"] syntax.

<?php
$json = '{"name": "Alice", "age": 25}';

$data = json_decode($json, true);

echo $data["name"]; // Alice
echo $data["age"];  // 25
?>

Challenge

Easy

Read a line of input containing a JSON object representing a book's information (e.g., {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925}).

Then read two more inputs:

A string key1 representing the first key to access
A string key2 representing the second key to access

To convert the JSON string into an associative array, use the built-in json_decode() function with true as the second argument:
$array = json_decode($jsonString, true);
The second argument true tells PHP to return an associative array instead of an object. Once decoded, you can access values by key just like any associative array, e.g. $array["title"].

Create an associative array from the JSON input, then:

Access and print the value associated with key1
Store the value associated with key2 in a variable called $info
Print the value stored in $info

Print each result on a separate line.

Example:

If the inputs are {"title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "year": 1925}, title, and author, the output should be:

The Great Gatsby
F. Scott Fitzgerald

If the inputs are {"name": "Laptop", "brand": "TechCo", "price": 999}, brand, and price, the output should be:

TechCo
999

Cheat sheet

To retrieve values from an associative array, use the key inside square brackets:

$person = [
    "name" => "Alice",
    "age" => 25,
    "city" => "Paris"
];

echo $person["name"]; // Alice
echo $person["age"];  // 25

The syntax is $array["key"]. Keys are case-sensitive.

You can store retrieved values in variables:

$product = [
    "title" => "Laptop",
    "price" => 999
];

$itemName = $product["title"];
echo $itemName; // Laptop

Use json_decode($jsonString, true) to convert a JSON string into an associative array. The second argument true tells PHP to return an array instead of an object:

$json = '{"name":"Alice","age":25}';
$data = json_decode($json, true);

echo $data["name"]; // Alice
echo $data["age"];  // 25

Try it yourself

<?php
// Read the JSON input
$jsonInput = trim(fgets(STDIN));

// Read the two keys
$key1 = trim(fgets(STDIN));
$key2 = trim(fgets(STDIN));

// TODO: Write your code below
// 1. Create an associative array from the JSON input using json_decode
// 2. Access and print the value associated with $key1
// 3. Store the value associated with $key2 in a variable called $info
// 4. Print the value stored in $info

?>

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction to PHP

The PHP Language Hello World!Tags and Statements Comments The new line

4Comparison & Logical Operators

Comparison Operators Equality & Identity Logical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic

7Arrays Part 2 - Associative

Intro to Associative ArraysAccessing Values by KeyModifying Values by Key Adding New Key-Value Pairs Check if Key Exists Recap - Key-Value Data Store

10Functions

Declaring & Calling Functions Function Parameters Returning Values Default Parameter Values Type Declarations for Params Return Type Declarations Variable Scope Recap - Creating Reusable Code