仅打印多维数组中包含特定值的行

Question

I have this array in PHP 5.2.3 :

$a = array (
    array("a","c","1");
    array("b","a","2");
    array("a","b","3");
    array("b","b","4");
    array("a","a","5");
);

and I would like to "select" (or create a new array) only the rows that have the first element "a". Like this :

"a","c","1"
"a","b","3"
"a","a","5"

How can I do this ?

EDIT :

<?php
    $a = array (
        array("a","c","1"),
        array("b","a","2"),
        array("a","b","3"),
        array("b","b","4"),
        array("a","a","5"),
    );

    $result = array_filter(
        $array,
        'testFirst'
    );

    print_r($result);
?>

I get this error Warning: array_filter() [function.array-filter]: The first argument should be an array in C:\wamp\www\keySearch\test.php on line 13

FINAL EDIT :

<?php
    $a = array (
        array("a","c","1"),
        array("b","a","2"),
        array("a","b","3"),
        array("b","b","4"),
        array("a","a","5"),
    );

    function testFirst($value) {
        return($value[0] == 'a');
    }

    $result = array_filter($a, testFirst);
    print_r($result);
?>

Answer 1

function testFirst($value) {
    return($value[0] == 'a');
}

$result = array_filter(
    $a,
    'testFirst'
);