[jfealy]

Masking is nice but as an alternative & still taking care not to remove leading blanks

q){x where 1b,1_not” “~’:x}s:” the quick brown fox ” ” the quick brown fox ”

Appears to be faster

q)S:10000000#s 
q)ts:5 {x where not n&prev n:null x}S 
197 100663904 
q)ts:5 {x where 1b,1_not" "~':x}S 
147 83886816

caching taking place?

q)ts:5 {x where not n&prev n:null x}S 
144 100663904 
q)ts:5 {x where 1b,1_not" "~':x}S 
148 83886816

[jfealy]

One thing to consider is that the seed value for the derived function means any leading blanks will be removed. Can use prev

q){x where not(&':)" "=x}s:" the quick brown fox " 
"the quick brown fox " 
q){x where not n&prev n:null x}s 
" the quick brown fox "

 

[jfealy]

(reverse sums::) is another method of generating a function composition https://code.kx.com/q/ref/compose/

q)'[reverse;sums]~(reverse sums::) 1b

 

The definition you see for reverse is the monad form of the K verb | . The colon is an aid to the interpreter, as unless immediately used, the verb always denotes it’s dyad.

e.g. you can see the difference here, where the first item returned is the reverse of the list, and the second item is a projection of the OR dyad.

q)(|:;|)@:1 2 3 3 2 1 |[1 2 3]

 

You can examine these in the .q namespace & there is further reading here https://code.kx.com/q/basics/exposed-infrastructure/#unary-forms

q)5#.q | :: neg | -: not | ~: null | ^: string| $:

 

In terms of the colons & their meanings, you can find more info & examples on this (and much more) in this excellent link https://github.com/quintanar401/DCoQ?tab=readme-ov-file#mystery-of-

 

 

[jfealy]

Arthur’s K solution for first n+1 numbers

k)n(|+) 1 fib:{x,sum -2#x}/[;0 1] // first n+2 aq:{first flip x(reverse sums::) 1} 
// first n+1 
q)ts fib 100000 1359 2097392 
q) 
q) 
q)ts aq 100000 14 6345952

[jfealy]

This might be of use – be sure to test first

https://github.com/jfealy/q/blob/master/mergeHdb.q

[jfealy]

Hi – yes it does. The corresponding logic block in .Q.en is

 

(`/:d,s)??,/?:'{$[0h=@x;,/x;x]}’t c // which translates to `:path/to/sym ? distinct raze distinct each (symlist from each column)

https://code.kx.com/q/ref/enum-extend/#filepath

 

[jfealy]

I believe that blocking/sync msg processing issue was fixed in v3.6 2021.03.04

[jfealy]

I would suggest running your examples above in the latest version of v4.0

Your version is 4yrs old – there will have been many improvements & fixes in that period

[jfealy]

Another alternative

q)ts:10000 {x#'x} 1+til 100 
207 63616 
q)ts:10000 {sums[-1_t]_where t:til 1+x}100 
106 130112 
q){x#'x}[1+til 100]~{sums[-1_t]_where t:til 1+x}100 
1b

However, when applied to a large vector, performance drops off as cut is expensive

q)ts {x#'x} 1+til 50000 
4099 14763251840 
q)ts {sums[-1_t]_where t:til 1+x}50000 
6454 31943645248

 

[jfealy]

Is this the behavior you’re looking for?

 

q)t:([] a:100?10;b:100?1.) 
q)f:{[x;it]c1:(-1_(>':) (it+1)>x`a),0b;
           c2: 0.5>abs log ratios next x`b;
           cond: $[1=it; c1; c1&c2];
           delete from x where cond|prev cond} 
q)count {f[;y]/[x]}/[t;1 2] 
56