Accumulators - Access additional list / column

Community Support
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1

https://learninghub.kx.com/forums/topic/accumulators-access-additional-list-column

I have a table created like below.

t:([]c: 30 40 25 20 4 4; c1: 10 20 5 25 5 4)

 

c2 is calculated Column (value from c1 or prev c2 is used based on evaluation).

prev value is taken as 0 for first row / if not available

 

Below are the calculations.

 

c c1 c2   c1>prev c2 OR prev c < prev c2 ? c1 prev c2
30 10 10   10>0 (True) OR No need of evaluation ? 10  
40 20 20   20>10(True) OR No need of evaluation ? 20  
25 5 20   5>20(False) OR 40<20(False) ?   20
20 25 25   25>20(True) OR No need of evaluation ? 25  
4 5 5   5>25(False) OR 20<25(True) ? 5  
4 4 4   4>5(False) OR 4<5(True) ? 4  
 

What I have till now

 

update c2: 0{?[y>x;y;0N]}c1 from t

 

How can I OR the condition prev c < prev c2 along with this? Can column c be accessed? Something like below.

 

update c2: 0{?[y>x|0^c <x;y;x]}c1 from t

 

2

Yes in that case an accumulator is needed. One method you could choose would be to pass a table through to accumulate while also allowing you to look back to previous rows:

q)update c2:1_@[;`c2]{y[`c2]:enlist $[(y[`c1][0]>last x[`c2]) or ((last x[`c])<last x[`c2]);y[`c1][0];last x`c2];x,y}/[enlist each {(1#0#x),x}update c2:0 from `c`c1#t] from t 
c c1 c2 
---------- 
30 10 10 
40 20 20 
25 5  20 
20 25 25 
4  5  5 
4  4  4 
4.5 3 4 
4.5 3.5 4
3

I was trying something like below. I am not sure if it works in all scenarios.

I will validate your solution as well and revert soon.

Thanks much for your patience. KX community support and response is just excellent

update c2: {?[((y>x)|(z<x));y;x]}[0;c1;0^prev c] from t 
c c1 c2 
---------- 
30 10 10 
40 20 20 
25 5  20 
20 25 25 
4  5  5 
4  4  4 
4.5 3 4 
4.5 3.5 4

 

 

4

Thanks rocuinneagain,

Works for most scenarios. I have added one more row at the end where I get a different result than expected. The value for c2 in last row should be 4 instead of 3.

t:(c: 30 40 25 20 4 4 1; c1: 10 20 5 25 5 4 3)

 

c c1 c2 c1>prev c2 OR prev c < prev c2 ? c1 prev c2
30 10 10 10>0 (True) OR No need of evaluation ? 10
40 20 20 20>10(True) OR No need of evaluation ? 20
25 5 20 5>20(False) OR 40<20(False) ? 20
20 25 25 25>20(True) OR No need of evaluation ? 25
4 5 5 5>25(False) OR 20<25(True) ? 5
4 4 4 4>5(False) OR 4<5(True) ? 4
1 3 4 3>4(False) OR 4<4(False) ? 4
  
update c2:fills ?[(c1>prev c1) or c<prev c1;c1;0N] from t 
c c1 c2 
-------- 
30 10 10 
40 20 20 
25 5 20 
20 25 25 
4  5  5 
4  4  4 
1  3  3
 

 

5

Looking at your expected c2 this logic may be what you are looking for:

 

q)update c2:fills ?[(c1>prev c1) or c<prev c1;c1;0N] from t 
c c1 c2 
-------- 
30 10 10 
40 20 20 
25 5 20 
20 25 25 
4  5  5 
4  4  4

 

6

changing c to prev[c] looks to be what was missing

 

q)update c2:fills ?[(c1>prev c1) or prev[c]<prev c1;c1;0N] from t 
c c1 c2 
-------- 
30 10 10 
40 20 20 
25 5 20 
20 25 25 
4  5  5 
4  4  4 
1  3  4

 

7

Somehow not being able to use the previous calculated value of c2 directly is causing fallout for different combination of data. Last value of c2 will be 4 as per the logic but we get 3.5

t:(c: 30 40 25 20 4 4 4.5 4.5; c1: 10 20 5 25 5 4 3 3.5)

 

c c1 c2 c1>prev c2 OR prev c < prev c2 ? c1 prev c2
30 10 10 10>0 (True) OR No need of evaluation ? 10
40 20 20 20>10(True) OR No need of evaluation ? 20
25 5 20 5>20(False) OR 40<20(False) ? 20
20 25 25 25>20(True) OR No need of evaluation ? 25
4 5 5 5>25(False) OR 20<25(True) ? 5
4 4 4 4>5(False) OR 4<5(True) ? 4
4.5 3 4 3>4(False) OR 4<4(False) ? 4
4.5 3.5 4 3.5>4(False) OR 4.5<4(False) ? 4
  
update c2:fills ?[(c1>prev c1) or prev[c]<prev c1;c1;0N] from t 
c c1 c2 
----------- 
30 10 10 
40 20 20 
25 5  20 
20 25 25
4  5  5 
4  4  4 
4.5 3 4 
4.5 3.5 3.5
 
8

Yes that’s much cleaner - as you only ever compute one value c2 and only look back 1 step. this will do exactly as you need.

9

From the Primary Accumulator list, select 0. From the First list, select Increment primary. From the Second list, select Use primary.Defines a custom accumulator operator. Accumulators are operators that maintain their state (e.g. totals, maximums, minimums, click test and related data) as documents . If you have access to Accumulator manager, you can access the Accumulator … To locate a record, you can sort each column alphabetically, …

10

Thanks for confirming. I checked both solutions and the result column matches exactly for my bigger data set.