wavg implementation detail

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1

https://learninghub.kx.com/forums/topic/wavg-implementation-detail

Hi, everyone.

I have some questions about wavg function.

0 wavg 5 / 5

5 wavg 5 / 5

2 wavg 2 3 7 / 4 5 2

3 wavg 3 / 3

 

According to the doc, the x and y of wavg[x;y] must both be numeric lists. But for these invalid inputs, wavg still yields some results. Could anyone help me understand the results of these invalid x and y?

What’s the behavior of wavg when x and y aren’t numeric lists or they don’t conform? It seems like avg y but I’m not sure.

If you know more about wavg’s implementation detail, please help me. Thanks.

2

Hello Ian,

Thank you for bringing this great question to our attention.

  • We can confirm that 
    0 wavg x
    should indeed be 0n. This is a bug and will be fixed by our team. Thank you for sharing this observation.
The following is an explanation for the other cases:
  • Atoms on both sides behave as if enlisted to single item vectors.
5 wavg 5  / 5 enlist[5] wavg enlist[5] /5
  • An atom on one side and a vector on the other behaves as if the atom is repeated to match the length of the vector.
2 wavg 2 3 7  / 4 2 2 2 wavg 2 3 7 /4  5 2 3 wavg 3  / 3 5 2 3 wavg 3 3 3 /3
We hope our feedback is helpful for you.

Thank you again for your contribution and engagement with our KX community. We look forward to more.

Kind regards,

Leah

3

Todays release kdb+4.0 2021.10.01 contains a fix for the issue in your first example:

q)0 wavg 5
0n

 

4

Hi Leah,

Thanks for your explanation.

So for the case “0 wavg x”, it is equivalent to (0*x)%0 => 0%0=0n. It really makes sense.

Thank you and your team again.