<?php

$object = (object) array(
    'data' => (object) array(
        44 => (object) array(
           'id' => 3.5795,
           'completed' => false,
           'name' => 'Lorem ipsum dolor.',
        ),
        45 => (object) array(
           'id' => 3.5796,
           'completed' => false,
           'name' => 'Lorem ipsum dolor.',
        ),
        46 => (object) array(
           'id' => 3.5797,
           'completed' => true,
           'name' => 'Lorem ipsum dolor.',
        ),
        47 => (object) array(
           'id' => 3.5798,
           'completed' => false,
           'name' => 'Lorem ipsum dolor.',
        ),
    )
);

$countTrue = 0;
$countFalse = 0;

foreach($object->data as $item)
{
    if($item->completed){
        $countTrue ++;
    } else {
        $countFalse++;
    }

}

echo "Itens como true: " . $countTrue; // 1
echo "<br>";
echo "Itens como false: " . $countFalse; // 3