Documentation

Find median values

This page documents an earlier version of InfluxDB. InfluxDB v2 is the latest stable version. See the equivalent InfluxDB v2 documentation: Find median values.

Use the median() function to return a value representing the 0.5 quantile (50th percentile) or median of input data.

Select a method for calculating the median

Select one of the following methods to calculate the median:

estimate_tdigest

(Default) An aggregate method that uses a t-digest data structure to compute an accurate 0.5 quantile estimate on large data sources. Output tables consist of a single row containing the calculated median.

Given the following input table:

_time_value
2020-01-01T00:01:00Z1.0
2020-01-01T00:02:00Z1.0
2020-01-01T00:03:00Z2.0
2020-01-01T00:04:00Z3.0

estimate_tdigest returns:

_value
1.5

exact_mean

An aggregate method that takes the average of the two points closest to the 0.5 quantile value. Output tables consist of a single row containing the calculated median.

Given the following input table:

_time_value
2020-01-01T00:01:00Z1.0
2020-01-01T00:02:00Z1.0
2020-01-01T00:03:00Z2.0
2020-01-01T00:04:00Z3.0

exact_mean returns:

_value
1.5

exact_selector

A selector method that returns the data point for which at least 50% of points are less than. Output tables consist of a single row containing the calculated median.

Given the following input table:

_time_value
2020-01-01T00:01:00Z1.0
2020-01-01T00:02:00Z1.0
2020-01-01T00:03:00Z2.0
2020-01-01T00:04:00Z3.0

exact_selector returns:

_time_value
2020-01-01T00:02:00Z1.0

The examples below use the example data variable.

Find the value that represents the median

Use the default method, "estimate_tdigest", to return all rows in a table that contain values in the 50th percentile of data in the table.

data
  |> median()

Find the average of values closest to the median

Use the exact_mean method to return a single row per input table containing the average of the two values closest to the mathematical median of data in the table.

data
  |> median(method: "exact_mean")

Find the point with the median value

Use the exact_selector method to return a single row per input table containing the value that 50% of values in the table are less than.

data
  |> median(method: "exact_selector")

Use median() with aggregateWindow()

aggregateWindow() segments data into windows of time, aggregates data in each window into a single point, and then removes the time-based segmentation. It is primarily used to downsample data.

To specify the median calculation method in aggregateWindow(), use the full function syntax:

data
  |> aggregateWindow(
    every: 5m,
    fn: (tables=<-, column) => tables |> median(method: "exact_selector")
  )

Was this page helpful?

Thank you for your feedback!


The future of Flux

Flux is going into maintenance mode. You can continue using it as you currently are without any changes to your code.

Flux is going into maintenance mode and will not be supported in InfluxDB 3.0. This was a decision based on the broad demand for SQL and the continued growth and adoption of InfluxQL. We are continuing to support Flux for users in 1.x and 2.x so you can continue using it with no changes to your code. If you are interested in transitioning to InfluxDB 3.0 and want to future-proof your code, we suggest using InfluxQL.

For information about the future of Flux, see the following: