how to find the intersection of a php array
To find the intersection of PHP arrays, use the built-in functions array_intersect(), array_intersect_key(), and array_intersect_assoc(). 1. array_intersect() compares the value to find the intersection, retaining the key of the first array; 2. array_intersect_key() only finds intersection according to the key name, and ignores the value; 3. array_intersect_assoc() compares the keys and values at the same time, and matches exactly; 4. Notes include: suitable for strings and complex types, indexes can be continuously processed by array_values(), direct parameters of most arrays, and case sensitivity of strings. Choosing the right function depends on the specific requirement.
It is actually not difficult to find the intersection of PHP arrays. The key is to understand the content you want to compare and the functions you use. PHP provides several built-in functions to handle the intersection problem between arrays, mainly array_intersect() and its variants.
1. Use array_intersect() to find the intersection of multiple arrays
This is the most commonly used function to find elements with the same key value in two or more arrays.
$array1 = [10, 20, 30, 40]; $array2 = [20, 40, 60, 80]; $result = array_intersect($array1, $array2);
The result will be:
Array
(
[1] => 20
[3] => 40
)Note: This function retains the key names in the first array and only compares whether the values are equal.
2. Use array_intersect_key() to find intersections by pressing the keys
If you need to find intersections based on key names , not values, then use this function.
$array1 = ['a' => 1, 'b' => 2, 'c' => 3]; $array2 = ['b' => 4, 'c' => 5, 'd' => 6]; $result = array_intersect_key($array1, $array2);
turn out:
Array
(
[b] => 2
[c] => 3
)It only looks at whether the key names are consistent, regardless of the corresponding value.
3. Use array_intersect_assoc() to compare keys and values at the same time
If you want to compare arrays more accurately, both the keys and the values are consistent , use this function.
$array1 = ['a' => 1, 'b' => 2, 'c' => 3]; $array2 = ['a' => 1, 'b' => 99, 'c' => 3]; $result = array_intersect_assoc($array1, $array2);
turn out:
Array
(
[a] => 1
[c] => 3
)Because only these two elements have the same key and value.
4. Common precautions and usage tips
These functions still apply if the array contains strings or other complex types.
If you want the returned array index to be contiguous, you can add
array_values()to process it.To find the intersection of multiple arrays, you only need to pass it in the function in sequence, for example:
array_intersect($arr1, $arr2, $arr3, $arr4);
These functions are case sensitive and pay special attention to strings if they are involved.
Basically these are the methods. Which function you choose depends on whether you want to press "value", "key" or "key value" to find the intersection. Although these functions are simple, you can only avoid being trapped after understanding the differences clearly.
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