median() function
median()
returns the median _value
of an input table or all non-null records
in the input table with values that fall within the 0.5 quantile (50th percentile).
Function behavior
median()
acts as an aggregate or selector transformation depending on the
specified method
.
- Aggregate: When using the
estimate_tdigest
orexact_mean
methods,median()
acts as an aggregate transformation and outputs the average of non-null records with values that fall within the 0.5 quantile (50th percentile). - Selector: When using the
exact_selector
method,meidan()
acts as a selector selector transformation and outputs the non-null record with the value that represents the 0.5 quantile (50th percentile).
Function type signature
(<-tables: stream[A], ?column: string, ?compression: float, ?method: string) => stream[A] where A: Record
Parameters
column
Column to use to compute the median. Default is _value
.
method
Computation method. Default is estimate_tdigest
.
Available methods:
- estimate_tdigest: Aggregate method that uses a t-digest data structure to compute an accurate median estimate on large data sources.
- exact_mean: Aggregate method that takes the average of the two points closest to the median value.
- exact_selector: Selector method that returns the row with the value for which at least 50% of points are less than.
compression
Number of centroids to use when compressing the dataset.
Default is 0.0
.
A larger number produces a more accurate result at the cost of increased memory requirements.
tables
Input data. Default is piped-forward data (<-
).
Examples
Use median as an aggregate transformation
import "sampledata"
sampledata.float()
|> median()
Use median as a selector transformation
import "sampledata"
sampledata.float()
|> median(method: "exact_selector")
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