Performance difference: Table.TransformColumns with function or New step after all data developped

[fmerieux]

Hello everyone,

This is just about personal curiosity and understanding 😀

I've created some steps where a function is needed to iterate through grouped rows in order to apply steps for each grouped rows 

Step 1 : Group the rows and aggregate with "All rows" column
#"GroupRows" = Table.Group(Source, {"Field1", "Field2"}, {{"All", each _, type table }})

Step 2: Create custom function

  #"CreateFunction" = (#"Tbl" as table) as table=>

let...

in...

Step 3: Apply custom function to the "All rows" field

#"ApplyFunction " = Table.TransformColumns( #"GroupRows",{"All", each #"! Create custom Function"(_)})

My question is: 

Let's say I'd like to add a Table.SelectRows(...)  step

Is there a big performance difference between

• adding the step within the Step2 within custom function
• adding the step later on once all data are developped

Thanks for reading this and all possible answers 🙂

Have a great day

[v-yalanwu-msft]

Hi, @fmerieux ;

Is your problem solved?  If so, kindly mark the proper reply as a solution to help others having the similar issue and close the case. If not, let me know and I'll try to help you further.

Best Regards,
Community Support Team _ Yalan Wu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[v-yalanwu-msft]

Hi, @fmerieux ;

Avoid calculated columns if you can. They're often not necessary and just end up bloating your model.

You could try to Create a new measure...

If the above one can't help you get the desired result, please provide some sample data in your tables (exclude sensitive data) with Text format and your expected result with backend logic and special examples. It is better if you can share a simplified pbix file. You can refer the following link to upload the file to the community. Thank you.

How to upload PBI in Community

Best Regards,
Community Support Team _ Yalan Wu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[lbendlin]

Implement two queries with the respective steps

Run Query Diagnostics on the last step of each query

Compare the query plans.