Get associative array (cat_slug => cat_name) in WordPress

category_array.php

<?php
// Category array
function chaoz_cat_array($term='portfolio_cat') {
    $cats = get_terms(array(
        'taxonomy' => $term,
        'hide_empty' => true
    ));
    $cat_array = array();
    $cat_array['all'] = esc_html__('All', 'gullu');
    foreach ($cats as $cat) {
        $cat_array[$cat->slug] = $cat->name;
    }
    return $cat_array;
}