change dataset-type on column

Hi, I have a dataset wich can have different types on one column dipending on the system it returns from. When I get the dataset from the system the user can search the column and this is handled with the filter-attribute. If the user make a search with '5' I return all the strings wich starts with a '5', but if the column-type is of integer the result returns alls values bigger than 5. Depending on the filterstring I get an error that i cant make the operation with the type int.

 

How can I solve this problem

best regards!!