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  • trait KeywordsStable extends AnyRef

    Keywords to mark aggregate expressions on and unifications of attributes.

    Keywords to mark aggregate expressions on and unifications of attributes.

    // Aggregates on any attribute type
Person.age(count).get.map(_.head ==> 3)         // count of asserted `age` attribute values
Person.age(countDistinct).get.map(_.head ==> 3) // count of asserted distinct `age` attribute values
Person.age(max).get.map(_.head ==> 38)          // maximum `age` value (using `compare`)
Person.age(min).get.map(_.head ==> 5)           // maximum `age` value (using `compare`)
Person.age(rand).get.map(_.head ==> 25)         // single random `age` value
Person.age(sample).get.map(_.head ==> 27)       // single sample `age` value (when single value, same as random)

// Aggregates on any attribute type, returning multiple values
Person.age(distinct).get.map(_.head ==> Vector(5, 7, 38)) // distinct `age` values
Person.age(max(2)).get.map(_.head ==> Vector(38, 7))      // 2 maximum `age` values
Person.age(min(2)).get.map(_.head ==> Vector(5, 7))       // 2 minimum `age` values
Person.age(rand(2)).get.map(_.head ==> Stream(5, ?))      // 2 random `age` values (values can re-occur)
Person.age(sample(2)).get.map(_.head ==> Vector(7, 38))   // 2 sample `age` values

// Aggregates on number attributes
Person.age(sum).get.map(_.head ==> 50)                  // sum of all `age` numbers
Person.age(avg).get.map(_.head ==> 16.66666667)         // average of all `age` numbers
Person.age(median).get.map(_.head ==> 7)                // median of all `age` numbers
Person.age(stddev).get.map(_.head ==> 15.107025591499)  // standard deviation of all `age` numbers
Person.age(variance).get.map(_.head ==> 228.2222222222) // variance of all `age` numbers
    Definition Classes
    api
  • AggrCoalesce
  • AggrInt
  • AggrKw
  • Kw
  • avg
  • bi
  • count
  • countDistinct
  • distinct
  • max
  • maxs
  • median
  • min
  • mins
  • rand
  • rands
  • sample
  • samples
  • stddev
  • sum
  • unify
  • v1
  • variance

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 ()
returns

Value of Attribute type

Source
Keywords.scala
Linear Supertypes
AggrCoalesce, AggrKw, Kw, AnyRef, Any
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median
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Inherited from AggrCoalesce

Inherited from AggrKw

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