PHP - Count all elements of an Array that Satisfy a Condition

Well, without seeing the code, so generally speaking, if you're going to split them anyway, you might as well do that up-front?

<?php
// getting all the results.
$products = $db->query('SELECT name FROM foo')->fetchAll();

$div1 = array_filter($products, function($product) {
    // condition which makes a result belong to div1.
    return substr('X', $product->name) !== false;
});

$div2 = array_filter($products, function($product) {
    // condition which makes a result belong to div2.
    return substr('Y', $product->name) !== false;
});

printf("%d elements in div1", count($div1));
printf("%d elements in div2", count($div2));

// then print the divs. No need for ifs here, because results are already filtered.
echo '<div id="a">' . PHP_EOL;
foreach( $div1 as $product ) {
   echo $product->name;
}
echo '</div>';

echo '<div id="b">' . PHP_EOL;
foreach( $div2 as $product ) {
   echo $product->name;
}
echo '</div>';

That being said: you should take notice of the comment which says "This is normally faster in SQL", because it is the more sane approach if you want to filter the values.

EDIT: Changed the name of the variables to adapt the variable names in the example code.

Use an array-filter: http://www.php.net/manual/en/function.array-filter.php

array array_filter ( array $input [, callable $callback = "" ] )

Iterates over each value in the input array passing them to the callback function. If the callback function returns true, the current value from input is returned into the result array. Array keys are preserved.

<?php
function odd($var)
{
    // returns whether the input integer is odd
    return($var & 1);
}

function even($var)
{
    // returns whether the input integer is even
    return(!($var & 1));
}

$array1 = array("a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
$array2 = array(6, 7, 8, 9, 10, 11, 12);

echo "Odd :\n";
print_r(array_filter($array1, "odd"));
echo "Even:\n";
print_r(array_filter($array2, "even"));
?>

But be aware, this is a loop though, and your the SQL query will be faster.