Understanding functions for parent-child hierarchies in DAX

DAX provides five functions to help users manage data that is presented as a parent-child hierarchy in their models. With this functions a user can obtain the entire lineage of parents a row has, how many levels has the lineage to the top parent, who is the parent n-levels above the current row, who is the n-descendant from the top of the current row hierarchy and is certain parent a parent in the current row hierarchy?

Parent-child functions in DAX

The following table contains a Parent-Child hierarchy on the columns: EmployeeKey and ParentEmployeeKey that is used in all the functions examples.

EmployeeKey ParentEmployeeKey
112
14 112
3 14
11 3
13 3
162 3
117 162
221 162
81 162

In the above table you can see that employee 112 has no parent defined, employee 14 has employee 112 as manager (ParentEmployeeKey), employee 3 has employee 14 as manager and employees 11, 13, and 162 have employee 3 as manager. The above helps to understand that employee 112 has no manager above her/him and she/he is the top manager for all employees shown here; also, employee 3 reports to employee 14 and employees 11, 13, 162 report to 3.

The following table presents the available functions, a brief description of the function and an example of the function over the same data shown above.

PATH function (DAX) - Returns a delimited text with the identifiers of all the parents to the current row, starting with the oldest or top most until current.

EmployeeKey ParentEmployeeKey Path
112 112
14 112 112|14
3 14 112|14|3
11 3 112|14|3|11
13 3 112|14|3|13
162 3 112|14|3|162
117 162 112|14|3|162|117
221 162 112|14|3|162|221
81 162 112|14|3|162|81

PATHLENGTH function (DAX) - Returns the number of levels in a given PATH(), starting at current level until the oldest or top most parent level. In the following example column PathLength is defined as ‘=PATHLENGTH([Path])’; the example includes all data from the Path() example to help understand how this function works.

EmployeeKey ParentEmployeeKey Path PathLength
112 112 1
14 112 112|14 2
3 14 112|14|3 3
11 3 112|14|3|11 4
13 3 112|14|3|13 4
162 3 112|14|3|162 4
117 162 112|14|3|162|117 5
221 162 112|14|3|162|221 5
81 162 112|14|3|162|81 5

PATHITEM function (DAX) - Returns the item at the specified position from a PATH() like result, counting from left to right. In the following example column PathItem - 4th from left is defined as ‘=PATHITEM([Path], 4)’; this example returns the EmployeKey at fourth position in the Path string from the left, using the same sample data from the Path() example.

EmployeeKey ParentEmployeeKey Path PathItem - 4th from left
112 112
14 112 112|14
3 14 112|14|3
11 3 112|14|3|11 11
13 3 112|14|3|13 13
162 3 112|14|3|162 162
117 162 112|14|3|162|117 162
221 162 112|14|3|162|221 162
81 162 112|14|3|162|81 162

PATHITEMREVERSE function (DAX) - Returns the item at position from a PATH() like function result, counting backwards from right to left.
In the following example column PathItemReverse - 3rd from right is defined as ‘=PATHITEMREVERSE([Path], 3)’; this example returns the EmployeKey at third position in the Path string from the right, using the same sample data from the Path() example.

EmployeeKey ParentEmployeeKey Path PathItemReverse - 3rd from right
112 112
14 112 112|14
3 14 112|14|3 112
11 3 112|14|3|11 14
13 3 112|14|3|13 14
162 3 112|14|3|162 14
117 162 112|14|3|162|117 3
221 162 112|14|3|162|221 3
81 162 112|14|3|162|81 3

PATHCONTAINS function (DAX) - Returns TRUE if the specified item exists within the specified path. In the following example column PathContains - employee 162 is defined as ‘=PATHCONTAINS([Path], "162")’; this example returns TRUE if the given path contains employee 162. This example uses the results from the Path() example above.

EmployeeKey ParentEmployeeKey Path PathContains - employee 162
112 112 FALSE
14 112 112|14 FALSE
3 14 112|14|3 FALSE
11 3 112|14|3|11 FALSE
13 3 112|14|3|13 FALSE
162 3 112|14|3|162 TRUE
117 162 112|14|3|162|117 TRUE

Important

In SQL Server 2012 Analysis Services, the Vertipaq in-memory analytics engine does not support the definition of parent-child hierarchies; however, the DAX language provides a set of functions that allows users to explore parent-child hierarchies and to use these hierarchies in formulas.