Extract Task Summary Name from Task Name column using TaskWBS

[SDM_1997]

Hi All,
Have a requirement to extract the "Tasks Summary Names" from a column called Task Name based on the TaskWBS column's value.
Our data is extracted from MS Project Online, using the api call in this format => https://<tenantname>.sharepoint.com/sites/pwa/_api/Projectdata/Tasks

Now, all Tasks that have subtasks are called as Task Summary Names. That is understood by the WBS value.
So, if WBS value is "blank", then that is the top most task, "Task 1", under which all tasks are present. If the value of a task, "Task 2", is "1", then the task summary of "Task 2" is "Task 1". Similarly, if there is a subtask under "Task 2" as "T 3" with the WBS value of 1.1, then summary name of "T 3" is "Task 2" and so on.
Something like this: - 

Now, in Power BI, extracting the Tasks table means that it is extracting all TaskNames as simple tasks and only way to differentiate is to use the TaskWBS table.
We have data in the below format: - 

ProjectName	TaskName	TaskWBS	Text Before Delimiter
AS01	AS01
AS01	memo PHF writing data TTT mtg	3
AS01	memo PHF review	4
AS01	T18m DLPG data treatment	2.2	2
AS01	global project management (TDT, mtg,..)	1
AS01	T9m	2.4	2
AS01	T12m	2.5	2
AS01	T18m	2.6	2
AS01	T24m	2.7	2
AS01	T24m DLPG	2.3	2
AS01	T20m	2.8	2
AS01	T24m	2.9	2
AS01	T24m DOPG	2.1	2
AS01	Stability plan 2-8°C	2
AS01	T18m DLPG lab	2.1	2
HRD - i88	HRD - i88
HRD - i88	Project Management	1
HRD - i88	Project Milestones	1.1	1
HRD - i88	Start of Project	1.1.1	1.1
HRD - i88	Implementation of Project	1.1.2	1.1
HRD - i88	work shop prod	1.1.3	1.1
HRD - i88	Phase 0 document	1.1.4	1.1
HRD - i88	Revue document	1.1.5	1.1
HRD - i88	Effectivi	1.1.7	1.1
HRD - i88	Formation	1.1.6	1.1

 
Now, we have Project Name, Task Name and TaskWBS from the source. As seen, the Task WBS value repeats itself as the Project changes since it only denotes task level.

The Text Before Delimiter is a custom column, I created to extract the WBS values that we need to get the Summary Names of its corresponding Task.  Formula - Table.AddColumn(#"Filtered Rows", "Text Before Delimiter", each Text.BeforeDelimiter([TaskWBS], ".", {0, RelativePosition.FromEnd}), type text)

Now, currently using a column called "TaskIsSummary", I am able to filter out all Task Names that are summaries. In a separate table. Like this: - 

So, currently I want to use this filtered table to get my data in the following format: - 

The Task Summary Name is the expected column output.
As in the above pic, the Task Names are repeating now besides the subtasks to denote its parent task.
I am able to achieve this using PQ, by merging the new table with the existing table (Linking Project IDs of both and TaskWBS from new table with Text before Delimiter column in the original table, so basically 4 columns linked together). But I am aware that merging has performance costs while refreshing.
Hence, if this output is possible as a DAX measure, would be better for performance I guess.
Please Help
Thanks!

[SDM_1997 · Accepted solution]

Update - I was not able to find any solution as a DAX measure.
Therefore, I stuck with my Power Query solution only.
But instead of doing this merging of Linking Project IDs of both tables and TaskWBS from new table with Text before Delimiter column in the original table in the Dataset itself, I moved this transformation to a Dataflow.
This improved the performance significantly. In the Dataflow, this merging takes hardly 10 seconds.