Returns the string form of this GroupBy.
The string form of this GroupBy.
The GroupBy format is:
CopyC#
if no depth has been set.
"<i>grouping-key-name</i>"
The format:
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is used if depth has been specified.
"<i>grouping-key-name</i>:<i>depth</i>"
The string:
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is returned if the grouping key is a dimension named Region
with a grouping level of 2 (that is, two levels below the root of
the dimension hierarchy).
Region:2