median
molecule.boilerplate.api.KeywordsStable.median
trait median extends AggrCoalesce
Median of attribute values.
Apply median keyword to attribute to return median of attribute values of entities matching the molecule.
for {
_ <- Match.sKeywords.insert(1, 2, 4)
_ <- Match.score(median).get.map(_.head ==> 2)
} yield ()
OBS: When it comes to an even number of values, Datomic has a special implementation of median that is different from the one described on the Wiki entry on the median function.
Datomic calculates the median of even number of values as the average of the two middle numbers rounded down to nearest whole number
for {
_ <- Match.sKeywords.insert(1, 2, 3, 4)
_ <- Match.score(median).get.map(_.head ==> 2) // (2 + 3) / 2 = 2.5 rounded down to 2
} yield ()
With decimal numbers this can go wrong:
for {
_ <- Match.sKeywords.insert(1.0, 2.5, 2.5, 3.0)
_ <- Match.score(median).get.map(_.head ==> 2) // (2.5 + 2.5) / 2 = 2.5 rounded down to 2 (This is wrong and bug report has been filed)
} yield ()
Attributes
- Returns
-
Value of Attribute type
- Source
- Keywords.scala
- Graph
-
- Supertypes
- Known subtypes
-
object median.type
In this article