使Jquery每次对一个 进行计算，同时影响页面上的其他人

I want look at the total size of a set of columns in a table and then set their width to the average of their widths. Jquery below works great if there's only one table on the page. However, in some cases there will be more than one table on the page. Their widths need to be calculated individually.I want look at the total size of a set of colum