How to output keys in php two-dimensional array

In PHP, a two-dimensional array refers to an array containing multiple arrays. Each subarray can contain one or more key-value pairs, making them very flexible and capable of providing very powerful functionality to our applications. However, some developers will encounter difficulties when we need to output the keys of a two-dimensional array. Therefore, this article will introduce how to output keys in a two-dimensional array.

1. What is a two-dimensional array

In PHP, array is an important data structure, and arrays can be used to store multiple values. Two-dimensional arrays can be used when multiple arrays need to be stored. In a two-dimensional array, each element is an array and can contain multiple key-value pairs. Among them, each element (subarray) can have a different key name, and the key name can be any legal string, because the key name is a unique identifier used to identify the subarray.

The following is an example two-dimensional array:

$people = array(
    array("name" => "Tom", "age" => 20),
    array("name" => "Jerry", "age" => 23),
    array("name" => "Mickey", "age" => 25)
);

In the above code, we created a $people array, which contains three sub-arrays, each sub-array represents a person, Contains their name and age information.

2. How to output two-dimensional array keys

In order to output the keys in a two-dimensional array, we need to use some functions and syntax in PHP. The following are introduced respectively:

1. Use the foreach statement

Through the foreach statement, you can traverse each element in the array, and store the key and value of the current element in the loop variables $key and $ respectively. value. Therefore, when traversing a two-dimensional array, we can use two nested foreach statements to traverse, where the outer loop traverses each sub-array and the inner loop traverses the keys of each sub-array.

The sample code is as follows:

foreach ($people as $person) {
    foreach ($person as $key => $value) {
        echo $key . "<br/>";
    }
}

In the above code, the outer foreach loop traverses three sub-arrays, the inner foreach loop traverses the keys in each sub-array, and stores the current key name in variable $key and output.

2. Use the array_keys function

If we only need to output all the keys in a two-dimensional array, we can use the array_keys function. The array_keys function will return a new array consisting of all the keys in the array. So, once we have this new array, we can output it using a foreach statement.

The sample code is as follows:

$keys = array_keys($people[0]);
foreach ($keys as $key) {
    echo $key . "<br/>";
}

In the above code, we first use the array_keys function to get all the key names in the first sub-array, and then traverse the new array through the foreach statement to output each key name.

3. Summary

This article introduces how to output the keys in a two-dimensional array. If you want to output the values ​​in a two-dimensional array, you can use a similar method, just replace the key name with the value. As you can see, using the foreach statement and the array_keys function is the most common approach. It should be noted that when outputting the key name, we can also output the corresponding value, which requires using another syntax. For details, please refer to the relevant PHP documentation.

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