PHP removes null values ​​from array

foreach( $arr as $k=>$v){
 if( !$v )
 unset( $arr[$k] );
}
?>

And I feel pretty good about it, but it’s not very efficient. I’ve tried it before, first converting $arr to an object, and then using the characteristics of the object to delete it, because: foreach is the current operation. The array is copied. Every time a foreach is operated, a variable is copied. If there are too many foreachs in the page, it will be a big consumption.

While wandering around on the Internet, I was surprised to see someone suggesting using array_filter. I opened the manual and took a look, and found that I had been guarding a treasure mountain but didn't know how to use it. The function of the array_filter function is to use the callback function to filter the array. I always thought that the callback function can be used to process it, but I didn't find that there is a sentence in the PHP manual. If there is no callback function, the default is to delete the items with a value of false in the array.

$entry = array(
 0 => 'foo',
 1 => false,
 2 => -1,
 3 => null,
 4 => ''
 );
print_r(array_filter($entry));
?>

Output value: Array ( [0] => foo [2] => -1 ) It seems that I still need to read more manuals in the future...just like array_slice, it is also a good thing. Too bad I never noticed it before. Attachment: Another example

$strDelCodes = "A;B;;C;;C;D;;;D;D";
$rsArray = array_values ​​(array_unique (array_diff (split (";", $strDelCodes), array (""))));

The values ​​stored in the array $rsArray are: A B C D The array_values() function returns an array containing all key values ​​in the given array, but does not retain the key names. The array_diff() function returns an array of differences between two arrays. This array contains all keys that are in the array being compared, but are not in any of the other argument arrays. The array_unique() function removes duplicate values ​​from an array and returns the resulting array. When the values ​​of several array elements are equal, only the first element is retained and the other elements are deleted. The key names in the returned array remain unchanged. The array_merge() function merges two or more arrays into one array. If there are duplicate key names, the key value of the key will be the value corresponding to the last key name (the later one will overwrite the previous one). If the array is numerically indexed, the key names are re-indexed consecutively.