How do you multiply values in one map with the values in another?

Question

If you have two maps (one is mutable, the other is immutable), how would you multiply the values of one with the corresponding values of the other?

For example:

val testA = scala.collection.mutable.Map("£2" -> 3, "£1" -> 0, 
                  "50p" -> 4, "20p" -> 0, "10p" -> 0, "5p" -> 0)
val testB = scala.collection.immutable.Map("£2" -> 2, "£1" -> 1, 
                  "50p" -> 0.5, "20p" -> 0.2, "10p" -> 0.1, "5p" -> 0.05)

Expecting a result of:

val total = scala.collection.immutable.Map("£2" -> 6, "£1" -> 0, 
                  "50p" -> 2, "20p" -> 0, "10p" -> 0, "5p" -> 0)`

score 2 · Accepted Answer · answered Apr 24 '17 at 15:28

2

You can use map to map each value to that value multiplied by the lookup result on testB (or 1.0, if none found)

testA.map { case (k, v) => (k, v * testB.getOrElse(k, 1.0)) }

answered Apr 24 '17 at 15:28

Tzach Zohar

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Excellent! Thank you very much. – Patrick White Apr 24 '17 at 15:53
1

See also: http://stackoverflow.com/questions/7076128/best-way-to-merge-two-maps-and-sum-the-values-of-same-key - same question (with addition instead of multiplication), with some other interesting answers (specifically, using Scalaz's Semigroup) – Tzach Zohar Apr 24 '17 at 15:54

How do you multiply values in one map with the values in another?

1 Answers1