QQ - How do I flag records that contain numeric data for a specific field?

I have a field that has a mix of numeric and string data in it - I can't work with the records that have the numeric data, so i want to flag them so that I can remove them from calculations - how do i do this?

We can approach this problem using the ICAST function.    ICAST will cast any fully numeric data to an integer, but any alphanumeric data as null. In the example below, ICAST2 contains only numeric data - all other data has been mapped as null:

We can now apply the null data as a filter on StartStation Name (i.e., keeping only data that couldn't be mapped to a numeric field) and we end up with a cleaned StartStation Name that doesn't contain any numeric data: