Power Query Custom function for running total

I've been trying to write a custom function in power query but keep getting errors, I've decided on a running total,

so i can do that proved the column names are the the same ;

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but this is no use if the column names are not 'unit' or whatever, so I tried the following for a percentage increase,

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And I can select the query add colum; invoke custome function and put in whatever columns I need as current and prevoious, so thoght I should be able to do the same fort List.Sum( List.FirstN , the problem seems to be the source,
I've tried ;

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and uiing 'Any' then thpe 'Source' in as that parameter, but no good, any suggestion,I've attached the workbook with attemps and errors.

Richard

Yes, but you need the values as a list, so List.FirstN( Source [Values] , N value) , 3 , I tried using source within
the function but it won't allow it, so I have to get the values to sum as a list.

Richard.

Thanks,


RD

Originally Posted by rorya

FirstN takes 2 arguments, not 3. What are Start and Amount supposed to be in that call?

I' mistakenly deducted from reputation this was by accident, can a moderator reverse this.

Richard.