call function with multiple value kdb/q

  • A+

I have a function declaration:

func:{[id;time] select last synp from synp_t where instr_id = id, tp_time < time} 

where instr_id has type i and tp_time has type v.

For example, func[8;05:00:11] works fine and gives me value 17.55.

However, if I try func[8 1;05:00:11 07:10:59], I get:

'length ERROR: incompatible lengths (different lengths of operands for synchronized operation or table columns lengths are not the same 

What I want to get is, for example, 17.55 9.66.

Same error will pop up as well if I do select res:func_demo[id;time]from tab, where tab is table with two column of instr_id and tp_time.

I guess enlist could possibly resolve the problem, but I don't know exactly how to use it. How could I fix this issue?


I'll recommend using aj to get the results, looking at your query it looks like you want the last price for the given id and smaller than the input time.

q)func:{[id;time] aj[`instr_id`tp_time; ([] instr_id:id;tp_time: time);synp_t]} q)func[1 1 2;05:00:11 07:10:59 10:10:00] 

with each-both you are calling the function n times and selecting the data n times. aj is one of the powerful features Kdb provides for the asof prices.

Actually, you don't need func function, you can directly get the results using aj.

aj[`instr_id`tp_time; update instr_id:id, tp_time: time from tab;synp_t] 


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