php join array

$arr = array('Hello','World!','Beautiful','Day!');
echo join(", ",$arr);

<?php

$arr = array('Hello','World!','Beautiful','Day!');

echo join(" ",$arr);

?> 

Definition and Usage
The join() function returns a string from the elements of an array.

The join() function is an alias of the implode() function.

Note: The join() function accept its parameters in either order. However, for consistency with explode(), you should use the documented order of arguments.

Note: The separator parameter of join() is optional. However, it is recommended to always use two parameters for backwards compatibility.

Syntax
join(separator,array)
  
Example
Join array elements with a string:

<?php
$arr = array('Hello','World!','Beautiful','Day!');
echo join(" ",$arr);
?>
  
Output:
Hello World! Beautiful Day!

$array1 = [1, 5, 64, 2, 6];
$array2 = [2, 1, 8, 3];

//Method 1:
array_filter($array1, function($_){
    global $array2;
  return in_array($_, $array2);
}); // Output: [0 => 1, 3 => 2]

//Method 2:
array_intersect($array1, $array2); //Output: [0 => 1, 3 => 2]

Combina los elementos de uno o más arrays juntándolos de modo que los valores de uno se anexan al final del anterior. Retorna el array resultante.