How to display posts by meta value, unique way

There is a custom post type and in the back-end there's a list of posts for it. The list contains columns of meta_values of custom fields associated with the post (see back-end on site). That was done using filters. The first column is a "week" column.
The values of the column are multiplied. For example there are multiple rows of "Week 4", "Week 3" etc. How to display only one "Week" row - so e.g. "Week 4" should be one row with all the values of all posts with meta_key "week" value of "Week 4" in their respective columns.