Basic usage

[Karim Douieb]

Hi all, I am trying to use Algebird in some basic context. I just want to create a function op that takes an array of a certain type (Integer in the following case, but I want it to work for string or any other basic types as well). The function just print the summation of the element in the array. 

  import com.twitter.algebird._

  val dataInt: Array[Int]= Array(1, 1, 2, 2, 3, 3, 4, 4, 5, 5)

  op(dataInt)

  def op[A: Monoid]( xs: Array[A]): Unit = {

   val m: Monoid[A] = implicitly[Monoid[A]]

   val res = xs.fold( m.zero )( m.plus )

   println("res = " + res)

 }

this is giving me the following error

[error] .../src/main/scala/algebird.scala:36: value zero is not a member of Monoid[A]

[error]     val res = xs.fold( m.zero )( m.plus )

If I replace Monoid by Ring then it works fine for an array of Int but then there is no way to use it with an array of String since there is no Ring type class for String in Algebird. How can I fix this?

I am pretty new to Scala so sorry if I am missing something obvious.

[Oscar Boykin]

I don't think algebird is on your classpath.

In the repo:

./sbt algebird-core/console

scala>  import com.twitter.algebird._

import com.twitter.algebird._

scala> 

scala>   val dataInt: Array[Int]= Array(1, 1, 2, 2, 3, 3, 4, 4, 5, 5)

dataInt: Array[Int] = Array(1, 1, 2, 2, 3, 3, 4, 4, 5, 5)

scala>   op(dataInt)

<console>:15: error: not found: value op

                op(dataInt)

                ^

scala> 

scala>   def op[A: Monoid]( xs: Array[A]): Unit = {

     |    val m: Monoid[A] = implicitly[Monoid[A]]

     |    val res = xs.fold( m.zero )( m.plus )

     |    println("res = " + res)

     |  }

op: [A](xs: Array[A])(implicit evidence$1: com.twitter.algebird.Monoid[A])Unit

scala> op(dataInt)

res = 30

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Oscar Boykin :: @posco :: http://twitter.com/posco

[Vincent Ohprecio]

Here are the instructions to get Algebird running in the REPL:

https://github.com/twitter/algebird/wiki/Algebird-Examples-with-REPL