How to get columns from php two-dimensional array

In PHP language, array is a commonly used data structure. A two-dimensional array means that each element in the array is also an array. When processing a two-dimensional array, sometimes you need to remove a certain column. This article will introduce how to remove a column of a two-dimensional array in PHP.

1. Use loop traversal

To take out the columns of a two-dimensional array, the simplest way is to use a loop to traverse the array. You can first loop through a column of all elements in the array, and then combine these columns into a new array. The following code is an example:

$students = array( 
array('name'=>'Alice', 'age'=>18, 'score'=>89), 
array('name'=>'Bob', 'age'=>19, 'score'=>92), 
array('name'=>'Cathy', 'age'=>18, 'score'=>91), 
array('name'=>'David', 'age'=>20, 'score'=>87), 
); 

$scores = array(); 
foreach ($students as $student) { 
    $scores[] = $student['score']; 
} 

print_r($scores);

The above code will take out the score column of all elements in the two-dimensional array $students and form it into a new array $scores. Here a foreach loop is used to traverse the array, the corresponding score value is taken out for each array element, and added to the new array $scores.

2. Use the array_column function

PHP provides the array_column function, which can easily extract a column of a two-dimensional array. The sample code is as follows:

$students = array( 
array('name'=>'Alice', 'age'=>18, 'score'=>89), 
array('name'=>'Bob', 'age'=>19, 'score'=>92), 
array('name'=>'Cathy', 'age'=>18, 'score'=>91), 
array('name'=>'David', 'age'=>20, 'score'=>87), 
); 

$scores = array_column($students, 'score'); 

print_r($scores);

The above code uses the array_column function to take out the score column of all elements in the two-dimensional array $students and form it into a new array $scores. Among them, the first parameter is a two-dimensional array, and the second parameter is the column name to be extracted.

It should be noted that the array_column function requires PHP version 5.5.0 and above, otherwise an error will be reported.

3. Use the array_map function

In addition to the array_column function, you can also use the array_map function to extract columns from a two-dimensional array. The following code is an example:

$students = array( 
array('name'=>'Alice', 'age'=>18, 'score'=>89), 
array('name'=>'Bob', 'age'=>19, 'score'=>92), 
array('name'=>'Cathy', 'age'=>18, 'score'=>91), 
array('name'=>'David', 'age'=>20, 'score'=>87), 
); 

$scores = array_map(function($student) { 
    return $student['score']; 
}, $students); 

print_r($scores);

The above code uses the array_map function to take out the score column of all elements in the two-dimensional array $students and form it into a new array $scores. Among them, the first parameter is the callback function, and the second parameter is the array to be operated on.

It should be noted that the efficiency of the array_map function is relatively low and may cause performance problems when processing large-scale arrays.

Among several ways to retrieve columns, the most commonly used method is to use the array_column function. In addition to fetching columns, the array_column function can also fetch the values ​​of specified columns to form a new array, and can use another index column as the key of the new array. These functions are very practical and can improve efficiency in actual development.

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