# 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"),
)
``````

### Linux Package Signing Key Rotation

All signed InfluxData Linux packages have been resigned with an updated key. If using Linux, you may need to update your package configuration to continue to download and verify InfluxData software packages.

For more information, see the Linux Package Signing Key Rotation blog post.