Very Slow data transformation steps

[Vikas_J]

Hello Community,

I have a set of excel based data sets ( ~ 15 excel files with substantial data). i want to bring this data to Power BI. The data in Excel is not well structured hence after i import data to Power Bi , i am applying transformation steps on the data to bring it to shape( for each file)

This is where the things are getting very slow. There are almost 20 data trasnformation steps required on each excel file. And for each step i enter it is taking very long to execute. Its seems for every transformation Power Bi tries to fetch new data from the source file and then run the transformation steps. Is this necessary. ? Is there a way to tell Power Bi to only work with data that has been imported in the first step of the query. 

Thanks in Adavance

[Idrissshatila]

Hello @Vikas_J ,

Power query works as you do the transformation and it save the steps then everytime you refresh, it bring the data from the source and go through the applied steps.

this is how power query works, and it won't pull data without applying the steps.

[Vikas_J]

If i add a transformation step to the query , for each step as minor as moving a location of a column, it is taking very long to process the transformation step. what could be the reason for this and how can i improve the speed for each step processing.