Kdb fby select 具有多元函数？

Question

如何在 kdb 中使用 fby 对带有多个参数的函数执行 select 语句？

我想要的是这样的：

t:([] price:1000?1f; sym:`AAPL; qty:3.0; open:0.20);
select from t where open<({exec x wavg y};qty;price) fby sym

无需做

t:update avgPrice:qty wavg price by sym from t;
t:select from t where avgPrice>open;

Answer 1

小样品台，多种测试：

q)t:([] price:15?10f; sym:15?`A`P`L; qty:15?3; open:15?10f);
q)t
price     sym qty open
---------------------------
3.614587  P   2   4.329653
8.378739  P   1   0.4506864
0.5421134 L   0   0.3795818
1.635727  A   0   9.475303
6.417787  L   1   0.7403326
6.655573  P   0   9.941467
8.064934  P   0   4.265147
4.316783  A   1   3.447288
9.054219  A   1   4.368897
3.741311  P   1   5.678812
7.319251  A   0   8.729202
4.999804  P   2   9.133432
7.846789  L   0   3.920599
6.721702  L   0   5.564439
7.074448  L   2   3.351027

您的版本：

q)select from (update avgPrice:qty wavg price by sym from t) where avgPrice>open
price     sym qty open      avgPrice
------------------------------------
3.614587  P   2   4.329653  4.891472
8.378739  P   1   0.4506864 4.891472
0.5421134 L   0   0.3795818 6.855561
6.417787  L   1   0.7403326 6.855561
8.064934  P   0   4.265147  4.891472
4.316783  A   1   3.447288  6.685501
9.054219  A   1   4.368897  6.685501
7.846789  L   0   3.920599  6.855561
6.721702  L   0   5.564439  6.855561
7.074448  L   2   3.351027  6.855561

与

fby

：

q)select from t where open<({x[;0] wavg x[;1]};flip (qty;price)) fby sym
price     sym qty open
---------------------------
3.614587  P   2   4.329653
8.378739  P   1   0.4506864
0.5421134 L   0   0.3795818
6.417787  L   1   0.7403326
8.064934  P   0   4.265147
4.316783  A   1   3.447288
9.054219  A   1   4.368897
7.846789  L   0   3.920599
6.721702  L   0   5.564439
7.074448  L   2   3.351027

检查结果是否匹配：

q)a:delete avgPrice from select from (update avgPrice:qty wavg price by sym from t) where avgPrice>open
q)b:select from t where open<({x[;0] wavg x[;1]};flip (qty;price)) fby sym
q)a~b
1b