CODEWITHSUNDEEP
scala
titan
titan

Reputation: 122

Modifying an array of tuples in Scala

I am new to Scala and would appreciate any help regarding the following code:

var exp = (-3).to(2, 1) 
var out = exp.map(i => java.lang.Float.floatToIntBits(math.pow(i, 2).toFloat))

Now, I want to write the following code:

for (i <- 0 until exp.length)
{if(exp(i) < 0) 
    {out(i) = out(i) >> exp(i).abs}
}

that is, I want to modify elements of the out vector depending on the elements of the exp vector by having a one-to-one mapping between the two vectors. I can't find a single online source which can help me do this. Please help.

Upvotes: 1

Views: 130

Answers (4)

elm
elm

Reputation: 20415

The extra iteration can be avoided by adding the shifting to the lambda function either by exp(i) if negative or by 0 (no effect) otherwise, like this,

var out = exp.map { i => 
  val f = java.lang.Float.floatToIntBits(math.pow(i, 2).toFloat) 
  f >> (if (i < 0) -i else 0)
}

Note also 

def step(i: Int) = if (i < 0) -i else 0

so that we can simplify the solution above as follows,

var out = exp.map { i => 
  java.lang.Float.floatToIntBits(math.pow(i, 2).toFloat) >> step(i)
}

Upvotes: 0

Gavin
Gavin

Reputation: 6470

Or make the transformation explicit and arguably more readable by putting it in a function then just having a single map operation.

def fn(i: Int): Int = {
  val o = java.lang.Float.floatToIntBits(math.pow(i, 2).toFloat)
  if (i < 0) o >> i.abs
  else o
}

exp.map(fn)

Upvotes: 0

Alexandr Dorokhin
Alexandr Dorokhin

Reputation: 850

The vector is immutable collection, you can't modify it, but you can create new one. For this, use for yield comprehension: 

val res = for (i <- 0 until exp.length)
  yield if(exp(i) < 0)
          out(i) >> exp(i).abs
        else
          out(i)

or just convert your vector to an array:

val out = exp.map(i => 
  java.lang.Float.floatToIntBits(math.pow(i, 2).toFloat)
).toArray

and modify your array.

Upvotes: 1

Shadowlands
Shadowlands

Reputation: 15074

The following should work:

out.zip(exp) map { case (o,e) => if (e < 0) o >> e.abs else o }

Upvotes: 1

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