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Dicken's avatar
Dicken
Post Prodigy
8 months ago
Solved

List Generate Average as record;

  Hi, can someone explain what is happening here;   I have a standard accumulaton, with two outcomes  one for the sum and one for average ;  let alist = List.Numbers( 1, 20 ,1 ) in List.Genera...
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  • PhilipTreacy's avatar
    PhilipTreacy
    8 months ago

    Dicken 

     

    I'm not sure what you are asking here.

     

    Clearly in the code z and y are always the same.

     

    But what is this?  It makes no sense.  Where are you getting this from?

     

     z / 2   <>    z = y/2

     

    You can't say a thing (z/2) is not equal (or equal) to another thing (z=y/2). 

     

    You can't have an assignment on one side of a logical test like this

     

    Again not sure how esle to explain this other than how I have.

     

     z / 2   <>    z = y/2 makes no sense mathematically and I don't know what you are trying to do there.

     

    Phil

     

Zanqueta's avatar
Zanqueta
Super User
8 months ago

Hi Dicken,

 

Let me know if thats it are you expecting for:

 

Script tested: 

let
    alist = List.Numbers(1, 20, 1),
    result = List.Generate(
        () => [x = 1, asum = alist{0}, avg = alist{0}],
        each [x] < List.Count(alist),
        each [
            x = [x] + 1,
            asum = [asum] + alist{[x]-1},
            avg = [asum] / [x]
        ]
    )
in
    result

 

My oppinion:

 

First Case (Works as Expected):

avg = asum / x

 
Here, avg depends on the current value of asum and x, which have already been updated in the same iteration. So at each step:
  • asum = cumulative sum up to current x
  • avg = cumulative sum divided by current count
    This gives the correct running average.

Second Case (Incorrect Result):

avg = ([avg] + alist)

Here, you are using the previous value of avg and adding the new element, then dividing by x. This introduces a logical error:
  • avg is not the sum; it is already an average from the previous step.
  • Adding alist{x-1} to an average does not produce a correct cumulative sum.
  • Then dividing by x again compounds the error.
Essentially, you are mixing average logic with incremental sum logic, which breaks the calculation.
 
Why does the second formula fail?
Because avg is not a sum, so adding a new element to it does not represent the cumulative total. The correct formula must always reference the cumulative sum (asum), not the previous average.
 

If this response was helpful in any way, Iā€™d gladly accept a šŸ‘much like the joy of seeing a DAX measure work first time without needing another FILTER.

Please mark it as the correct solution. It helps other community members find their way faster (and saves them from another endless loop šŸŒ€.