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For example
case class Blah(security: String, price: Double) val myList = List(Blah("a", 2.0), Blah("b", 4.0)) val sum = myList.sum(_.price) // does not work What is the syntax for obtaining the sum?
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Scala List sum() method with example. The sum() method is utilized to add all the elements of the stated list. Return Type: It returns the sum of all the elements of the list.
Syntax for defining a Scala List. val variable_name: List[type] = List(item1, item2, item3) or val variable_name = List(item1, item2, item3) A list in Scala is mostly like a Scala array. However, the Scala List is immutable and represents a linked list data structure. On the other hand, Scala array is flat and mutable.
Try this:
val sum = myList.map(_.price).sum Or alternately:
val sum = myList.foldLeft(0.0)(_ + _.price) You appear to be trying to use this method:
def sum [B >: A] (implicit num: Numeric[B]): B and the compiler can't figure out how the function you're providing is an instance of Numeric, because it isn't.
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Scalaz has this method under a name foldMap. The signature is:
def M[A].foldMap[B](f: A => B)(implicit f: Foldable[M], m: Monoid[B]): B Usage:
scala> case class Blah(security: String, price: Double) defined class Blah scala> val myList = List(Blah("a", 2.0), Blah("b", 4.0)) myList: List[Blah] = List(Blah(a,2.0), Blah(b,4.0)) scala> myList.foldMap(_.price) res11: Double = 6.0 B here doesn't have to be a numeric type. It can be any monoid. Example:
scala> myList.foldMap(_.security) res12: String = ab If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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