wavg implementation detail

Community Support
1

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

Hi Ian, 

Great question! We’re working on an answer for you. 

Thanks for your contribution and getting us thinking!

Laura

3

Thanks for your reply and looking forward to the answer!

4

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

5

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.

 

6

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

q)0 wavg 5
0n