WISH: I would like a getFilterValue method property on the column object

[dwlovell]

This is similar to being able to provide getSortValue, I would like to be able to provide my own method for returning the filter value for a particular column cell.

I am using a json object for the actual values in the dataset. I then use a renderer to display custom UI and getSortValue for making sure sorting works. However I cannot use filter because the value it tries to use is the value of the json object, not the sub-property that has the value to filter with.