why sv needs ,' here?

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1

https://learninghub.kx.com/forums/topic/why-sv-needs-here

I have the below trades table in my q session:

 

q)meta trades 
c    | t f a 
-----| ----- 
time | p 
sym  | s   g 
src  | s   g
price| f 
size | i

 

 

Then, why does it need each both for the sv function when x and y are joined already and then passed into sv:

 

q)update symsrc:{` sv'(x,'y)}[sym;src] from 1#trades 
time                          sym src price size symsrc 
-------------------------------------------------------- 
2023.06.04D08:00:49.248000000 ORCL L 40.67 3984 ORCL.L 

q)update symsrc:{-1 .Q.s1 x,y; ` sv'(x,'y)}[sym;src] from 1#trades `ORCL`L 
time                          sym src price size symsrc 
-------------------------------------------------------- 
2023.06.04D08:00:49.248000000 ORCL L 40.67 3984 ORCL.L

 

2

You’ll get a type error without the each, because you need to create a scalar from each vector (i.e. each pair of symbols)

 

q)t:([]sym:`ORCL`APPL;src:`L`R) t 
sym src 
-------- 
ORCL L 
APPL R 

q) update symsrc:` sv (sym,'src) from t 
'type [0] 
update symsrc:` sv (sym,'src) from t ^ 

q) update symsrc:` sv'(sym,'src) from t 
sym src symsrc 
--------------- 
ORCL L ORCL.L 
APPL R APPL.R

 

Bonus tip - as shown above, you can avoid using a lambda by using parenthesis so the parser doesn’t interpret the comma as a new column statement.

3

David has already answered the question here, but it’s worth noting that you can do this operation very succinctly using .Q.dd:

q)update symsrc:.Q.dd'[sym;src]from trades 

time                          sym src price size symsrc 
-------------------------------------------------------- 
2023.06.04D10:22:20.088377000 ORCL L 40.67 3984 ORCL.L