# weather data is incorrect? **URL:** \ **Category:** Academy Support\ **Tags:** kx-academy\ **Created:** [December 8, 2025, 12:16pm UTC](https://forum.kx.com/t/weather-data-is-incorrect/15342 "2025-12-08T12:16:37Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![vjay.b5](https://avatars.discourse-cdn.com/v4/letter/v/f4b2a3/32.png) [@vjay.b5](https://forum.kx.com/u/vjay.b5)\ **Post date:** [December 8, 2025, 12:16pm UTC](https://forum.kx.com/t/weather-data-is-incorrect/15342/1 "2025-12-08T12:16:38Z")
When min date is 2009.01.01 , how come the result below has a 2008.12.27? ![image](https://us1.discourse-cdn.com/flex002/uploads/kx/original/1X/e99a4e2e155efb85f91201c21a542f75f5c48be3.png) ---
**Author:** ![mmcparland](https://sea2.discourse-cdn.com/flex002/user_avatar/forum.kx.com/mmcparland/32/54_2.png) [@mmcparland](https://forum.kx.com/u/mmcparland)\ **Post date:** [December 8, 2025, 3:13pm UTC](https://forum.kx.com/t/weather-data-is-incorrect/15342/2 "2025-12-08T15:13:27Z")
Hi @vjay.b5 When q groups dates using `7 xbar date`, it divides the data into **7-day buckets** , each bucket labelled by the **start of that 7-day period**. Because the data begins on **2009.01.01** , but the natural 7-day alignment for q falls on **2009.01.03** , q aligns the buckets to that boundary. As a result, the first two dates— **2009.01.01** and **2009.01.02** —do not fill a complete 7-day group by themselves. q still includes them, but it assigns them to the bucket whose label is **2008.12.27** , which is simply _the start date of the 7-day period that includes 2009.01.01_. This label **does not mean data came from 2008.12.27** ; it’s only the calculated start of that 7-day interval. I hope this clears things up and if you have any questions about this, let me know! 🙂 ---
**Author:** ![vjay.b5](https://avatars.discourse-cdn.com/v4/letter/v/f4b2a3/32.png) [@vjay.b5](https://forum.kx.com/u/vjay.b5)\ **Post date:** [December 9, 2025, 5:07am UTC](https://forum.kx.com/t/weather-data-is-incorrect/15342/3 "2025-12-09T05:07:27Z")
Thanks Megan, that’s very helpful. But what do you mean by “ **the natural 7-day alignment for q falls on 2009.01.03** “ ? 2009.01.03 is Saturday (not Sunday) just curious how q determine the bucket period here automatically. (Am new to q/kdb perhaps am missing something) ---
**Author:** ![mmcparland](https://sea2.discourse-cdn.com/flex002/user_avatar/forum.kx.com/mmcparland/32/54_2.png) [@mmcparland](https://forum.kx.com/u/mmcparland)\ **Post date:** [December 9, 2025, 11:50am UTC](https://forum.kx.com/t/weather-data-is-incorrect/15342/4 "2025-12-09T11:50:48Z")
@vjay.b5 `a xbar b` returns the _largest multiple of `a` that is ≤ b_. So for example, say we have `7 xbar 2009.01.01` it will convert the date to internal integers from 2000.01.01 (the epoch). 2009.01.01 = 3288 days To find the **nearest multiple of 7** to **3288** : 3288 ÷ 7 = **469.714…** The closest two multiples to 7 are: 1. Lower multiple: 469 × 7 = 3283 (2008.12.27) 2. Upper multiple: 470 × 7 = 3290 (2009.01.03) `7 xbar date` groups dates into 7-day buckets aligned to multiples of 7 days since **2000.01.01** , producing week-based buckets like: 2008.12.27 2009.01.03 2009.01.10 I hope this helps!