Groups the rows of {0} by the values in the specified column,{1}, for each row. For each group, a record is constructed containing ...

Groups the rows of {0} by the values in the specified column,{1}, for each row.
    For each group, a record is constructed containing the key columns (and their values) along with any aggregated columns specified by {2}. 
    Note if multiple keys match the comparer, different keys may be returned. This function cannot guarantee to return a fixed order of rows.
    Optionally, {3} and {4} may also be specifed.