What is the use extract and compact function in php

A possible use for extract() is to import into the symbol table variables contained in an associative array returned by
<?php
/* Suppose that $var_array is an array returned from
   wddx_deserialize */
$size = "large";$var_array = array("color" => "blue",
                   "size"  => "medium",
                   "shape" => "sphere");extract($var_array, EXTR_PREFIX_SAME, "wddx");

echo "$color, $size, $shape, $wddx_size\n";
?>

The above example will output:

blue, large, sphere, medium

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compact — Create array containing variables and their values

Example #1 compact() example

<?php
$city  = "San Francisco";$state = "CA";$event = "SIGGRAPH";
$location_vars = array("city", "state");
$result = compact("event", "nothing_here", $location_vars);print_r($result);?>

The above example will output:

Array
(
    [event] => SIGGRAPH
    [city] => San Francisco
    [state] => CA
)