Standard deviation calculation through Power query

[Betty888]

Dear all, 

I have an issue with a Power BI File using big data sources. After a quick analysis, I realised that my DAX queries are the reason behind the slowness of my file, so I'm trying to convert most of my DAX queries to the Power query editor. 

I have an issue with the calcultion of Standard deviation for a DATA column that I have to calculate by Grouped data and I can't use the "Group by" function, I need to have an additional calumn containing the standard deaviation . 

Here below the DAX formula that was percectly working for me and that I want to convert to Power query : 

TRT_STD =
CALCULATE ( STDEV.S ( ASSESSMENT [DATA] ), ALLEXCEPT ( Table, Table[group.data] ) )

Thank you in advance for your help ! 

[ppm1]

Although sometimes it is necessary to pre-calculate stuff to improve performance, I would stick with DAX and optimize your model if necessary. This will make your calculations responsive to slicers and overall provide more flexibility in reporting/analysis. Is your model a star schema? How many values in your visual?

Pat