// Loop to find each variants ID
<? foreach ($variantsData as $variantData) {

    $variant = array(
        'id'            => $variantData['variation_id'],
    );
} ?>

// Output each variants ID
<? print_r( $variant['id'] ) ?>

// Loop to find each variants ID
<? foreach ($variantsData as $variantData) {

    $variant[] = array(
        'id'            => $variantData['variation_id'],
    );
} ?>

// Output each variants ID
<? print_r( $variant['id'] ) ?>