Deleting an element from an array in PHP

后端 未结 30 3358
时光说笑
时光说笑 2020-11-21 05:55

Is there an easy way to delete an element from an array using PHP, such that foreach ($array) no longer includes that element?

I thought that setting it

相关标签:
30条回答
  • 2020-11-21 06:34
      // Our initial array
      $arr = array("blue", "green", "red", "yellow", "green", "orange", "yellow", "indigo", "red");
      print_r($arr);
    
      // Remove the elements who's values are yellow or red
      $arr = array_diff($arr, array("yellow", "red"));
      print_r($arr);
    

    This is the output from the code above:

    Array
    (
        [0] => blue
        [1] => green
        [2] => red
        [3] => yellow
        [4] => green
        [5] => orange
        [6] => yellow
        [7] => indigo
        [8] => red
    )
    
    Array
    (
        [0] => blue
        [1] => green
        [4] => green
        [5] => orange
        [7] => indigo
    )
    

    Now, array_values() will reindex a numerical array nicely, but it will remove all key strings from the array and replace them with numbers. If you need to preserve the key names (strings), or reindex the array if all keys are numerical, use array_merge():

    $arr = array_merge(array_diff($arr, array("yellow", "red")));
    print_r($arr);
    

    Outputs

    Array
    (
        [0] => blue
        [1] => green
        [2] => green
        [3] => orange
        [4] => indigo
    )
    
    0 讨论(0)
  • 2020-11-21 06:34

    Solutions:

    1. To delete one element, use unset():
    unset($array[3]);
    unset($array['foo']);
    
    1. To delete multiple noncontiguous elements, also use unset():
    unset($array[3], $array[5]);
    unset($array['foo'], $array['bar']);
    
    1. To delete multiple contiguous elements, use array_splice():
    array_splice($array, $offset, $length);
    

    Further explanation:

    Using these functions removes all references to these elements from PHP. If you want to keep a key in the array, but with an empty value, assign the empty string to the element:

    $array[3] = $array['foo'] = '';
    

    Besides syntax, there's a logical difference between using unset() and assigning '' to the element. The first says This doesn't exist anymore, while the second says This still exists, but its value is the empty string.

    If you're dealing with numbers, assigning 0 may be a better alternative. So, if a company stopped production of the model XL1000 sprocket, it would update its inventory with:

    unset($products['XL1000']);
    

    However, if it temporarily ran out of XL1000 sprockets, but was planning to receive a new shipment from the plant later this week, this is better:

    $products['XL1000'] = 0;
    

    If you unset() an element, PHP adjusts the array so that looping still works correctly. It doesn't compact the array to fill in the missing holes. This is what we mean when we say that all arrays are associative, even when they appear to be numeric. Here's an example:

    // Create a "numeric" array
    $animals = array('ant', 'bee', 'cat', 'dog', 'elk', 'fox');
    print $animals[1];  // Prints 'bee'
    print $animals[2];  // Prints 'cat'
    count($animals);    // Returns 6
    
    // unset()
    unset($animals[1]); // Removes element $animals[1] = 'bee'
    print $animals[1];  // Prints '' and throws an E_NOTICE error
    print $animals[2];  // Still prints 'cat'
    count($animals);    // Returns 5, even though $array[5] is 'fox'
    
    // Add a new element
    $animals[ ] = 'gnu'; // Add a new element (not Unix)
    print $animals[1];  // Prints '', still empty
    print $animals[6];  // Prints 'gnu', this is where 'gnu' ended up
    count($animals);    // Returns 6
    
    // Assign ''
    $animals[2] = '';   // Zero out value
    print $animals[2];  // Prints ''
    count($animals);    // Returns 6, count does not decrease
    

    To compact the array into a densely filled numeric array, use array_values():

    $animals = array_values($animals);
    

    Alternatively, array_splice() automatically reindexes arrays to avoid leaving holes:

    // Create a "numeric" array
    $animals = array('ant', 'bee', 'cat', 'dog', 'elk', 'fox');
    array_splice($animals, 2, 2);
    print_r($animals);
    Array
    (
        [0] => ant
        [1] => bee
        [2] => elk
        [3] => fox
    )
    

    This is useful if you're using the array as a queue and want to remove items from the queue while still allowing random access. To safely remove the first or last element from an array, use array_shift() and array_pop(), respectively.

    0 讨论(0)
  • 2020-11-21 06:35

    unset() destroys the specified variables.

    The behavior of unset() inside of a function can vary depending on what type of variable you are attempting to destroy.

    If a globalized variable is unset() inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset() was called.

    <?php
        function destroy_foo()
        {
            global $foo;
            unset($foo);
        }
    
        $foo = 'bar';
        destroy_foo();
        echo $foo;
    ?>
    

    The answer of the above code will be bar.

    To unset() a global variable inside of a function:

    <?php
        function foo()
        {
            unset($GLOBALS['bar']);
        }
    
        $bar = "something";
        foo();
    ?>
    
    0 讨论(0)
  • 2020-11-21 06:36

    If you have to delete multiple values in an array and the entries in that array are objects or structured data, [array_filter][1] is your best bet. Those entries that return a true from the callback function will be retained.

    $array = [
        ['x'=>1,'y'=>2,'z'=>3], 
        ['x'=>2,'y'=>4,'z'=>6], 
        ['x'=>3,'y'=>6,'z'=>9]
    ];
    
    $results = array_filter($array, function($value) {
        return $value['x'] > 2; 
    }); //=> [['x'=>3,'y'=>6,z=>'9']]
    
    0 讨论(0)
  • 2020-11-21 06:37

    Also, for a named element:

    unset($array["elementName"]);
    
    0 讨论(0)
  • 2020-11-21 06:38

    There are different ways to delete an array element, where some are more useful for some specific tasks than others.

    Deleting a single array element

    If you want to delete just one array element you can use unset() or alternatively \array_splice().

    If you know the value and don’t know the key to delete the element you can use \array_search() to get the key. This only works if the element does not occur more than once, since \array_search returns the first hit only.

    unset()

    Note that when you use unset() the array keys won’t change. If you want to reindex the keys you can use \array_values() after unset(), which will convert all keys to numerically enumerated keys starting from 0.

    Code:

    $array = [0 => "a", 1 => "b", 2 => "c"];
    unset($array[1]);
              // ↑ Key which you want to delete
    

    Output:

    [
        [0] => a
        [2] => c
    ]
    

    \array_splice() method

    If you use \array_splice() the keys will automatically be reindexed, but the associative keys won’t change — as opposed to \array_values(), which will convert all keys to numerical keys.

    \array_splice() needs the offset, not the key, as the second parameter.

    Code:

    $array = [0 => "a", 1 => "b", 2 => "c"];
    \array_splice($array, 1, 1);
                       // ↑ Offset which you want to delete
    

    Output:

    [
        [0] => a
        [1] => c
    ]
    

    array_splice(), same as unset(), take the array by reference. You don’t assign the return values of those functions back to the array.

    Deleting multiple array elements

    If you want to delete multiple array elements and don’t want to call unset() or \array_splice() multiple times you can use the functions \array_diff() or \array_diff_key() depending on whether you know the values or the keys of the elements which you want to delete.

    \array_diff() method

    If you know the values of the array elements which you want to delete, then you can use \array_diff(). As before with unset() it won’t change the keys of the array.

    Code:

    $array = [0 => "a", 1 => "b", 2 => "c", 3 => "c"];
    $array = \array_diff($array, ["a", "c"]);
                              // └────────┘
                              // Array values which you want to delete
    

    Output:

    [
        [1] => b
    ]
    

    \array_diff_key() method

    If you know the keys of the elements which you want to delete, then you want to use \array_diff_key(). You have to make sure you pass the keys as keys in the second parameter and not as values. Keys won’t reindex.

    Code:

    $array = [0 => "a", 1 => "b", 2 => "c"];
    $array = \array_diff_key($array, [0 => "xy", "2" => "xy"]);
                                   // ↑           ↑
                                   // Array keys which you want to delete
    

    Output:

    [
        [1] => b
    ]
    

    If you want to use unset() or \array_splice() to delete multiple elements with the same value you can use \array_keys() to get all the keys for a specific value and then delete all elements.

    0 讨论(0)
提交回复
热议问题