array_map、array_filter、およびarray_reduceを使用したデータ変換をマスターします

使用array_map、array_filter和array_reduce可高效处理PHP数组。1. array_map用于转换数组每个元素，如将数字平方或字符串转整数；2. array_filter用于筛选符合条件的元素，如保留偶数或成年人年龄；3. array_reduce用于将数组归约为单个值，如求和或拼接字符串；三者可链式调用实现清晰的数据处理流程，提升代码可读性与可维护性，减少对foreach的依赖。

When working with arrays in PHP, transforming and processing data efficiently is a common need. Functions like array_map, array_filter, and array_reduce are powerful tools that allow you to manipulate arrays in a clean, functional programming style. Mastering these functions can simplify your code, reduce bugs, and make your logic more readable.

Here’s how each of these functions works and when to use them.

Transform Data with array_map

array_map applies a callback function to each element of one or more arrays and returns a new array with the transformed values. It doesn't modify the original array.

Use case: You want to modify every element in an array in a consistent way.

$numbers = [1, 2, 3, 4, 5];

$squared = array_map(function($n) {
    return $n ** 2;
}, $numbers);

// Result: [1, 4, 9, 16, 25]

You can also use it with built-in functions:

$strings = ['1', '2', '3'];
$integers = array_map('intval', $strings);

This is much cleaner than writing a foreach loop with manual pushing.

Tip: If you pass multiple arrays, array_map will pass corresponding elements to the callback. This is useful for combining arrays element-wise.

Filter Elements with array_filter

array_filter loops through an array and returns a new array containing only the elements that pass a given condition.

Use case: You want to remove unwanted elements based on a rule.

$numbers = [1, 2, 3, 4, 5, 6];

$evens = array_filter($numbers, function($n) {
    return $n % 2 === 0;
});

// Result: [2, 4, 6]

By default, array_filter preserves keys. If you want reindexed numeric keys, wrap it with array_values():

$evens = array_values(array_filter($numbers, fn($n) => $n % 2 === 0));

You can also filter associative arrays by key or value:

$ages = ['Alice' => 25, 'Bob' => 17, 'Charlie' => 30];

$adults = array_filter($ages, fn($age) => $age >= 18);
// Returns ['Alice' => 25, 'Charlie' => 30]

Reduce an Array to a Single Value with array_reduce

array_reduce walks through an array and builds up a single result by applying a callback function. It’s ideal for aggregations like sum, concatenation, or building complex structures.

Use case: You want to summarize or condense an array into one value.

$numbers = [1, 2, 3, 4];

$sum = array_reduce($numbers, function($carry, $item) {
    return $carry + $item;
}, 0);

// Result: 10

The third parameter is the initial value of $carry. If omitted, the first element is used (which can lead to bugs if the array is empty).

More advanced example: building a string from words:

$words = ['hello', 'world', 'php'];

$sentence = array_reduce($words, function($carry, $word) {
    return $carry === null ? $word : "$carry $word";
}, null);

// Result: "hello world php"

Or even transforming an array into an associative structure:

$pairs = [['name', 'Alice'], ['age', 25]];

$assoc = array_reduce($pairs, function($carry, $pair) {
    [$key, $value] = $pair;
    $carry[$key] = $value;
    return $carry;
}, []);

// Result: ['name' => 'Alice', 'age' => 25]

Combining the Three for Powerful Pipelines

One of the biggest advantages is that you can chain these functions to create readable data processing pipelines.

Example: Process a list of user ages, square each, keep only those over 100, then sum them.

$ages = [5, 10, 15, 20];

$result = array_reduce(
    array_filter(
        array_map(fn($age) => $age ** 2, $ages),
        fn($sq) => $sq > 100
    ),
    fn($carry, $item) => $carry + $item,
    0
);

// Step-by-step:
// map: [25, 100, 225, 400]
// filter: [225, 400]
// reduce: 625

While you could use loops, this functional style emphasizes what you're doing, not how—making the intent clearer.

Each of these functions encourages immutability and avoids side effects when used properly. They help you write more predictable, testable code.

Use array_map to transform, array_filter to select, and array_reduce to summarize. Combine them when needed, and you’ll find your array operations become much more expressive.

Basically, once you get comfortable with these three, you’ll reach for foreach a lot less.

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