Drop row_index from summarize output
Summarize doesn't do anything if len(data) == 0
Fixed error when constructing a DataFrame from 0 rows
Needed to update argument to pandas.DataFrame in construct_pandas_df
Only remove row_id column if it's found
Reorder output rows to count, unique, std, min, 25/50/75%, max, modes, prob_modes, where calculated
Resolved merge conflicts with remote updates to summarize
Only drop columns inplace if the argument is available, and return 'stat' column with a blank name to avoid column name duplication
Added test for summarize with 0 input rows
Don't need to return anything from drop_df (confirmed with Jay), and call to df_drop doesn't need to be assigned to a new value