GROUPBY The GROUPBY function is similar to the SUMMARIZE function. However, GROUPBY does not do an implicit CALCULATE for any extension columns that it adds. GROUPBY permits a new function, CURRENTGROUP(), to be used inside aggregation functions in the extension columns that it adds. GROUPBY attempts to reuse the data that has been grouped making it highly performant.
GROUPBY (table, [groupBy_columnName1], [name, expression]… )
Table – Any DAX expression that returns a table of data.
GroupBy_columnName – The name of an existing column in the table (or in a related table,) by which the data is to be grouped. This parameter cannot be an expression.
Name – The name given to a new column that is being added to the list of GroupBy columns, enclosed in double quotes.
Expression – Any DAX expression that returns a single scalar value, where the expression is to be evaluated for each set of GroupBy values.
A table with the selected columns for the groupBy_columnName arguments and the grouped by columns designated by the name arguments.