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 - 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 - 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 - 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 - 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 - 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 |