How to use map within Array[Array]

Question

I want to apply a simple anonymous function to every element in a Array[Array], and output a Array[Array]. This function basically convert all positive numbers into 1, all negatives -1.

I know how to do the same thing for Array, but not Array[Array]. Is there a way to unwrap it?

val data = Array(Array(1,2),Array(-1,-2))
data.map(x => x.map{if (y > 0.0) 1.0 else 0.0})

Your code doesn't compile, you need a y => before the if. Apart from that it should work fine. — Marth
– Marth, Commented Mar 3, 2018 at 23:53
I'm not very familiar with Scala, but you can in general compose a map function with itself to give you map2, which behaves as you require. — user1726343
– user1726343, Commented Mar 4, 2018 at 0:12

prayagupadhyay · Accepted Answer · 2018-03-04 00:03:40Z

4

first map would give you each Array[T], second map would give you each element in that array.

given,

scala> val data = Array(Array(1,2),Array(-1,-2))
data: Array[Array[Int]] = Array(Array(1, 2), Array(-1, -2))

here's how you can apply function on each elem of second array,

scala> data.map(_.map(elem => if (elem > 0) 1 else -1 ))
res0: Array[Array[Int]] = Array(Array(1, 1), Array(-1, -1))

You can also use collect,

scala> data.map(_.collect{case elem if elem > 0 => 1 case _ => -1 })
res1: Array[Array[Int]] = Array(Array(1, 1), Array(-1, -1))

To simplify the same work using a function,

scala> def plusOneMinusOne(x: Int) = if (x > 0) 1 else -1
plusOneMinusOne: (x: Int)Int

scala> data.map(_.map(plusOneMinusOne)) 
res3: Array[Array[Int]] = Array(Array(1, 1), Array(-1, -1))

edited Mar 4, 2018 at 0:03

answered Mar 3, 2018 at 23:57

prayagupadhyay

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