ClickHouse/docs/en/sql-reference/aggregate-functions/reference/entropy.md

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---
2022-04-03 23:05:35 +00:00
toc_priority: 302
---
# entropy {#entropy}
Calculates [Shannon entropy](https://en.wikipedia.org/wiki/Entropy_(information_theory)) of a column of values.
**Syntax**
``` sql
entropy(val)
```
**Arguments**
- `val` — Column of values of any type.
**Returned value**
- Shannon entropy.
Type: [Float64](../../../sql-reference/data-types/float.md).
**Example**
Query:
``` sql
CREATE TABLE entropy (`vals` UInt32,`strings` String) ENGINE = Memory;
INSERT INTO entropy VALUES (1, 'A'), (1, 'A'), (1,'A'), (1,'A'), (2,'B'), (2,'B'), (2,'C'), (2,'D');
SELECT entropy(vals), entropy(strings) FROM entropy;
```
Result:
``` text
┌─entropy(vals)─┬─entropy(strings)─┐
│ 1 │ 1.75 │
└───────────────┴──────────────────┘
```