differ applied on each day rather then the entire dataset

Community Support
1

I am trying to run this query : 

 

 

select diffDate:differ startDate from tab where date within(.z.d-2;.z.d-1)

 

 

I would expect to have this 

 

publishTime sym startDate difD
2024.01.10D00:00:01.014000000 test1 2024.01.11 1
2024.01.10D00:00:03.541000000 test1 2024.01.11 0
2024.01.10D00:01:46.222000000 test1 2024.01.11 0
2024.01.10D00:02:14.276000000 test1 2024.01.12 1
2024.01.10D00:02:22.306000000 test1 2024.01.12 0
2024.01.10D23:59:58.366000000 test1 2024.01.12 0
2024.01.11D00:00:00.875000000 test1 2024.01.12 0
2024.01.11D00:00:02.378000000 test1 2024.01.12 0
2024.01.11D00:00:35.445000000 test1 2024.01.12 0
2024.01.11D00:02:02.623000000 test1 2024.01.15 1
2024.01.11D00:02:06.133000000 test1 2024.01.15 0

 

 However, I get this (check the difD col around roll over day) 

 

publishTime sym startDate difD
2024.01.10D00:00:01.014000000 test1 2024.01.11 1
2024.01.10D00:00:03.541000000 test1 2024.01.11 0
2024.01.10D00:01:46.222000000 test1 2024.01.11 0
2024.01.10D00:02:14.276000000 test1 2024.01.12 1
2024.01.10D00:02:22.306000000 test1 2024.01.12 0
2024.01.10D23:59:58.366000000 test1 2024.01.12 0
2024.01.11D00:00:00.875000000 test1 2024.01.12 1
2024.01.11D00:00:02.378000000 test1 2024.01.12 0
2024.01.11D00:00:35.445000000 test1 2024.01.12 0
2024.01.11D00:02:02.623000000 test1 2024.01.15 1
2024.01.11D00:02:06.133000000 test1 2024.01.15 0

Is this expected. I thought differ and deltas are applied on the entire array of startDate no on each day.

2

differ is not one of the aggregations which will auto perform map-reduce

https://code.kx.com/q4m3/14_Introduction_to_Kdb+/#1437-map-reduce

In this case the operation is applied once per partition.

 

To have it operate on your full result set you can change your query to query the data from disk untouched and then perform the aggregation in memory:

select diffDate:differ startDate from select startDate from tab where date within(.z.d-2;.z.d-1)

 

3

Thanks 
I was looking for that link there. 
It’s not normal that they don’t clarify this whey they talk about delta/differ.