DOCAPI-7460: histogram function description #6235
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
BayoNet
added
comp-documentation
blinkov
suggested changes
Jul 31, 2019
| @@ -2,6 +2,44 @@ | |||
|
|
|||
| Some aggregate functions can accept not only argument columns (used for compression), but a set of parameters – constants for initialization. The syntax is two pairs of brackets instead of one. The first is for parameters, and the second is for arguments. | |||
|
|
|||
| ## histogram | |||
|
|
|||
| Calculates a histogram. | |||
There was a problem hiding this comment.
it's an adaptive histogram which is quite unusual and worth mentioning in the very beginning, also afaik it's not guaranteed to be 100% accurate
| histogram(number_of_bins)(values) | ||
| ``` | ||
|
|
||
| The functions uses [A Streaming Parallel Decision Tree Algorithm](http://jmlr.org/papers/volume11/ben-haim10a/ben-haim10a.pdf). It calculates the borders of histogram bins automatically, and in common case the widths of bins are not equal. |
There was a problem hiding this comment.
Borders are not just calculated, they are constantly adjusted along the way
| **Parameters** | ||
|
|
||
| `number_of_bins` — Number of bins for the histogram. | ||
| `values` — [Expression](../syntax.md#syntax-expressions) resulting in a data sample. |
There was a problem hiding this comment.
"data sample" sounds out of place, maybe "input values" or something?
|
|
||
| **Parameters** | ||
|
|
||
| `number_of_bins` — Number of bins for the histogram. |
There was a problem hiding this comment.
have you checked what happens you run this on table with less rows than number_of_bins? probably it's the upper limit for number of bins, not the guaranteed number
| SELECT histogram(5)(number + 1) FROM (SELECT * FROM system.numbers LIMIT 20) | ||
| ``` | ||
| ```text | ||
| ┌─histogram(5)(plus(number, 1))───────────────────────────────────────────┐ |
There was a problem hiding this comment.
probably can be visualised using bar(...) function, would be useful example
|
@BayoNet ping |
BayoNet
changed the title
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
I hereby agree to the terms of the CLA available at: https://yandex.ru/legal/cla/?lang=en
Category (leave one):