In KDB, for each ticker I’d like to get all the rows where signal=1 except the first occurrence in each ticker.

og:([]
    ticker:raze 5#/:(`AAPL`GOOGL`MSFT);
    date:raze 3#enlist 2023.01.01+til 5;
    price:45 46 47 48 49,100 102 101 103 105,200 201 199 202 205;
    volume:1000 1100 900 1200 1300,500 520 510 530 550,300 310 290 320 330;
    signal:0 0 1 1 0,0 1 1 1 0,0 0 0 1 1 / Example entry signals
 );

t:select from og where signal=1;
t:update valid:1b from t where date>(min;date) fby ticker;
t:select from t where valid;
show t: delete valid from t; / correct but verbose

q)og
ticker date       price volume signal
-------------------------------------
AAPL   2023.01.01 45    1000   0     
AAPL   2023.01.02 46    1100   0     
AAPL   2023.01.03 47    900    1     
AAPL   2023.01.04 48    1200   1     
AAPL   2023.01.05 49    1300   0     
GOOGL  2023.01.01 100   500    0     
GOOGL  2023.01.02 102   520    1     
GOOGL  2023.01.03 101   510    1     
GOOGL  2023.01.04 103   530    1     
GOOGL  2023.01.05 105   550    0     
MSFT   2023.01.01 200   300    0     
MSFT   2023.01.02 201   310    0     
MSFT   2023.01.03 199   290    0     
MSFT   2023.01.04 202   320    1     
MSFT   2023.01.05 205   330    1 

q)t
ticker date       price volume signal 
-------------------------------------
AAPL   2023.01.04 48    1200   1         
GOOGL  2023.01.03 101   510    1          
GOOGL  2023.01.04 103   530    1          
MSFT   2023.01.05 205   330    1        

I find my approach quite verbose, and I’m wondering if one can be terser and hopefully more efficient. Just for reference, the naive/incorrect select statement below gives an undesired result

q) select by ticker from og where date>date[first where signal=1] / incorrect
ticker| date       price volume signal
------| ------------------------------
AAPL  | 2023.01.05 49    1300   0     
GOOGL | 2023.01.05 105   550    0     
MSFT  | 2023.01.05 205   330    1