Add column to php array

In PHP, an array is a data structure that stores multiple values. Sometimes we need to add a column to an array, such as adding some additional information to the result set after a database query. This article will introduce different methods to add columns in PHP arrays.

Method 1: Use a loop to assign new columns

The first method is to use a loop to traverse the array and add a column value to each array element. For example, suppose we have the following array:

$persons = array(
  array('name' => 'Tom', 'age' => 24),
  array('name' => 'John', 'age' => 28),
  array('name' => 'Sarah', 'age' => 23)
);

Now we want to add a "gender" column for each person, with the value automatically determined based on their name. We can use the following code to solve it:

foreach ($persons as &$person) {
  $name = $person['name'];
  if (substr($name, -1) == 'a') {
    $person['gender'] = 'Female';
  } else {
    $person['gender'] = 'Male';
  }
}

In the above code, we used a foreach loop to iterate through the array elements of each person. In the loop, we add a "gender" column to each person's array element and assign a value to it.

It should be noted that the variable $person is passed by reference, so we use the & symbol. This ensures that when the element referenced by $person is modified in the loop, the elements in the original array are also modified.

Method 2: Use the array_map function to add columns

The second method is to use the built-in array_map function in PHP to add columns. The array_map function applies a function to each element in an array and returns a new array. For example, the following code:

$persons = array(
  array('name' => 'Tom', 'age' => 24),
  array('name' => 'John', 'age' => 28),
  array('name' => 'Sarah', 'age' => 23)
);

$gender_mapper = function($person) {
  $name = $person['name'];
  if (substr($name, -1) == 'a') {
    $person['gender'] = 'Female';
  } else {
    $person['gender'] = 'Male';
  }
  return $person;
};

$new_persons = array_map($gender_mapper, $persons);

In the above code, we define an anonymous function named $gender_mapper and use this function to call the array_map function. The function $gender_mapper accepts a $person array parameter, adds a "gender" column for each person, and finally returns the increased $person array.

It should be noted that the array_map function returns not the original array, but a new array. Therefore, we need to store the results in a new variable $new_persons.

Method 3: Use the array_walk function to add columns

The third method is to use the built-in array_walk function in PHP to add columns. The array_walk function traverses each element in the array and operates on the element in the accepted callback function, which can be modified directly on the original array.

$persons = array(
  array('name' => 'Tom', 'age' => 24),
  array('name' => 'John', 'age' => 28),
  array('name' => 'Sarah', 'age' => 23)
);

function add_gender(&$person) {
  $name = $person['name'];
  if (substr($name, -1) == 'a') {
    $person['gender'] = 'Female';
  } else {
    $person['gender'] = 'Male';
  }
}

array_walk($persons, 'add_gender');

In the above code, we define a function called add_gender and use this function to call the array_walk function. The function add_gender accepts a $person array parameter and adds a "gender" column for each person in the array.

It should be noted that the $person parameter in the function add_gender is passed by reference, which also means that we modified the elements of the $person array in the callback function.

Summary

The above introduces three different methods to add columns in PHP arrays. The first method is to use a loop to assign new columns, the second method is to use the array_map function, and the third method is to use the array_walk function. Depending on your specific needs and code implementation, you can choose one or more of these methods.

It should be noted that the above methods are all for associative arrays. For adding columns to ordinary arrays, just use the [] operator. For example:

$arr = array(1, 2, 3);
$arr[] = 4; // 数组末尾增加一列

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