> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dune.com/llms.txt
> Use this file to discover all available pages before exploring further.

# T-Digest functions

## Data structures

A T-digest is a data sketch which stores approximate percentile
information. The Trino type for this data structure is called `tdigest`.
T-digests can be merged, and for storage and retrieval they can be cast
to and from `VARBINARY`.

## Functions

#### merge()

**`merge(tdigest)`** → tdigest

Aggregates all inputs into a single `tdigest`.

#### values\_at\_quantile()

**`value_at_quantile(tdigest, quantile)`** → double

Returns the approximate percentile value from the T-digest, given the number `quantile` between 0 and 1.

#### values\_at\_quantiles()

**`values_at_quantiles(tdigest, quantiles)`** → array(double)

Returns the approximate percentile values as an array, given the input T-digest and an array of values between 0 and 1, which represent the quantiles to return.

#### tdigest\_agg()

**`tdigest_agg(x)`** → tdigest

Composes all input values of `x` into a `tdigest`. `x` can be of any numeric type.

**`tdigest_agg(x, w)`** → tdigest

Composes all input values of `x` into a `tdigest` using the per-item weight `w`. `w` must be greater or equal than 1. `x` and `w` can be of any numeric type.