How to find out values shared by some members

[cy163]

Hello ALL,

I have a table contains words extracted from documents which are belonging to a number of categories. Each category contains a number of documents. For each category, I want to find out those words which occur at least in N documents belonging to this category.

Category    DocID       Word       Freq      Tag
Art             A12         Paint        3           verb
Art             A12        Exhibition    5           noun
Art             A12         Show        2           verb
Art             A12          Ticket       4          noun

Art             B34         Exhibition   2          noun
Art             B34         Musum       3          noun
Art             B34         Contemporary   2      adj
Art             B34         Show               1      noun
Art             B34         Visitor             2       noun


Art             E97         gallery             3      noun
Art             E97         Show               3      noun
Art             E97         Exhibition         2       noun


Electronics    A32        Circuit           2       noun
Electronics    A32        IC                 2       noun
Electronics    A32        Factory         2       noun
Electronics    A32       Electronics      3       noun

Electronics    F11        HiFi               2     noun
Electronics    F11        IC                 2     noun
Electronics    F11        Circuit           2     noun

Electronics   C55         IC                 3      noun
Electronics   C55         Circuit           3      noun
Electronics   C55         Transmit        2      verb
Electronics   C55         Receive         5      verb

I have no idea on how to do this query.

Thanks