quantileDeterministic

Computes an approximate quantile of a numeric data sequence.

quantileDeterministic

Introduced in: v1.1.0

Computes an approximate quantile of a numeric data sequence.

This function applies reservoir sampling with a reservoir size up to 8192 and deterministic algorithm of sampling. The result is deterministic. To get an exact quantile, use the quantileExact function.

When using multiple quantile* functions with different levels in a query, the internal states are not combined (that is, the query works less efficiently than it could). In this case, use the quantiles function.

Syntax

quantileDeterministic(level)(expr, determinator)

Aliases: medianDeterministic

Parameters

• level — Optional. Level of quantile. Constant floating-point number from 0 to 1. We recommend using a level value in the range of [0.01, 0.99]. Default value: 0.5. At level=0.5 the function calculates median. Float*

Arguments

• expr — Expression over the column values resulting in numeric data types, Date or DateTime. (U)Int* or Float* or Decimal* or Date or DateTime
• determinator — Number whose hash is used instead of a random number generator in the reservoir sampling algorithm to make the result of sampling deterministic. As a determinator you can use any deterministic positive number, for example, a user id or an event id. If the same determinator value occurs too often, the function works incorrectly. (U)Int*

Returned value

Returns an approximate quantile of the specified level. Float64 or Date or DateTime

Examples

Computing deterministic quantile

Query

CREATE TABLE t (val UInt32) ENGINE = Memory;
INSERT INTO t VALUES (1), (1), (2), (3);

SELECT quantileDeterministic(val, 1) FROM t;

Response

┌─quantileDeterministic(val, 1)─┐
│                           1.5 │
└───────────────────────────────┘

See Also

• median
• quantiles