An array is a collection of objects that contain a group of variables stored under the same name. All the elements belong to the same data type, i.e. string, integers, or lists. Keys are unique in the case of both indexed and associative arrays.
The main difference between isset() and array_key_exists() function is that the array_key_exists() function will definitely tells if a key exists in an array.
array_reduce() Method: As the name suggests, an array_reduce() function reduces the array to a single value by performing the given operation. The array_reduce() applies the callback function to the elements of the array and gives output as a single value.
array_walk() Method: It applies a user-defined function to every member of an array. The array’s keys and values are parameters in the function. The array_walk() function is not affected by the internal array pointer of the array.