/**
 * arry:數(shù)組， length:多少長度為一組
*/
group_arry(arry, length) {
    let index = 0;
    let new_arry = [];
    if (arry.length > length) {
        while (index < arry.length) {
            new_arry.push(arry.slice(index, index += length));
	}
    } else {
        new_arry = [arry];
    }
        return new_arry;
}