Specify the column header names of the columns you wish to display in the mini report.

For instance, say you want to display a mini version of the ByCity report:

bycity_full

 

To select which columns, just use the column header names:

[rover_idx_report report_name="bycity" is_mini_report="true" report_selected_cities="Brewster,Chatham,Dennis,Eastham,Falmouth,Harwich" report_mini_columns="city,num sold listings,avg selling price"]

This report is generated:
bycity_mini