how to understand the below code

Community Support
,
1

https://learninghub.kx.com/forums/topic/how-to-understand-the-below-code

hi All,

I am new to q and have some issue in understanding the below code

 

.quantQ.stats.kendallTauRank:{[xS;yS]

    //xS,yS -- arrays of values to compare the rank

   // aggregate concordance statictics

  stats: sum raze {.quantQ.stats.concordanceRoutine/:[y;(1+x?y)_x]}[t] each t: flip(xS,yS);

 // return kendall's tau rank

:(stats[0]-stats[1])%0.5*count[xS]*count[xS]-1;

}

 

.quantQ.stats.concordanceRoutine return a tuple like 100b, 010b

 

my understanding is t is like (num1,num2) if so, what is the each right operation doing? in particular the x,y should be numeric value then how should i read the staff inside [y;(1+x?y)_x] based on the drop, it seems like x,y are still vector

 

2

Lets see what we can infer.

.quantQ.stats.kendallTauRank:{[xS;yS]   //xS,yS -- arrays of values to compare the rank   // aggregate concordance statictics   stats: sum raze {.quantQ.stats.concordanceRoutine/:[y;(1+x?y)_x]}[t] each t: flip(xS,yS);   // return kendall's tau rank   :(stats[0]-stats[1])%0.5*count[xS]*count[xS]-1;   }

flip(xS,yS) tells us that xS and yS must be same-width matrices otherwise there would be nothing to flip.

The binary lambda {.quantQ.stats.concordanceRoutine/:[y;(1+x?y)_x]} is projected on t, which thus becomes the y in the lambda.

The lambda could equally be written {y .quantQ.stats.concordanceRoutine/:(1+x?y)_x} from which it might be clearer how, with x set to t, the binary concordance routine is being iterated: each row of t against the rows that follow it.

Two ways to express the same iteration:

raze{.quantQ.stats.concordanceRoutine/:[y;(1+x?y)_x]}[t] each t t .quantQ.stats.concordanceRoutine'(1+til count t)_: t

Line 6 defines the result. Omitting the explicit Return : and the trailing semicolon would be better style. stats would be three integers; the difference could also be written -/[2#stats].