Passing same data to two or more methods in Scala

Question

I am trying to call two methods in main method and passing same data to both. Here second parameter is a two dimensional array with n rows and 2 columns. First method executes successfully but When call goes to second method with same data, array becomes null (all enteries set's to zero). I want to pass same data(array) to both methods. Note that value of first parameter (n) remains same. How can I pass same data to both methods? Code is given below.

object Demo {
  def main(args: Array[String]): Unit = {
    println("Enter number of process:");
    val n = scala.io.StdIn.readInt();
    var array: Array[Array[Double]] = Array.ofDim(n, 2)
    var bt: Double = 0
    var at: Double = 0
    for (i <- 0 to n - 1) {
      println("Enter BT for process: " + i);
      bt = scala.io.StdIn.readDouble();
      println("Enter AT for process: " + i);
      at = scala.io.StdIn.readDouble();
      array(i)(0) = at
      array(i)(1) = bt
    }
    One(n, array)
    Two(n, array)
  }
  def One(n: Int, data: Array[Array[Double]]): Unit = {
    var q = 0.0
    var arr = data
    arr = arr.sortBy(x => x(1))
    var arr_copy = arr
    var wt = new Array[Double](n)
    var a = new Array[Double](n)
    var tat = new Array[Double](n)
    var new_tat = new Array[Double](n)
    var new_wt = new Array[Double](n)
    var D_Sum = 0.0
    var sum = 0.0
    for (i <- 0 to n - 1) {
      a(i) = arr(i)(1)
    }
    for (i <- 0 to n - 1) {
      wt(i) = 0
    }
    var tracker = 0.0
    var li = 0
    var updated_TAT = 0.0
    do {
      D_Sum = 0.0
      arr = arr.filterNot(x => x(1) <= 0)
      for (i <- 0 to arr.size - 1) {
        D_Sum = D_Sum + arr(i)(1)
      }
      q = math.round(math.sqrt(arr.length * D_Sum * 1.49))
      for (i <- 0 to arr.size - 1) {
        if (tracker >= arr(i)(0)) {
          if (arr(i)(1) > q) { //if BT > quantum time
            arr(i)(1) -= q
            tracker = tracker + q
            for (j <- 0 to arr.size - 1) {
              if ((j != i) && (arr(j)(1) != 0))
                wt(j) += q
            }
          }
          else {
            for (j <- 0 to arr.size - 1) {
              if ((j != i) && (arr(j)(1) != 0)) {
                wt(j) += arr(i)(1)
              }
            }
            tracker = tracker + arr(i)(1)
            updated_TAT = tracker
            new_tat(li) = updated_TAT - arr_copy(i)(0)
            new_wt(li) = tracker - arr_copy(i)(1) - arr_copy(i)(0)
            li = li + 1
            arr(i)(1) = 0
          }
        }
      }
      sum = 0.0
      for (i <- 0 to arr.length - 1)
        sum = sum + arr(i)(1)
    } while (sum != 0)
    var avg_wt = 0.0
    var avg_tat = 0.0
    for (j <- 0 to n - 1)
      avg_wt += wt(j)
    for (j <- 0 to n - 1)
      avg_tat += new_tat(j)
    println("average waiting time= " + (avg_wt / n) + " Average turn around time= " + (avg_tat / n))
  }
  def Two(n: Int, data: Array[Array[Double]]): Unit = {
    var arr = data
    arr = arr.sortBy(x => x(1))
    var arr_copy = arr
    var q = 0.0
    var wt = new Array[Double](n)
    var a = new Array[Double](n)
    var tat = new Array[Double](n)
    var new_tat = new Array[Double](n)
    var new_wt = new Array[Double](n)
    var sum = 0.0
    for (i <- 0 to n - 1) {
      a(i) = arr(i)(1)
    }
    for (i <- 0 to n - 1) {
      wt(i) = 0
    }
    var tracker = 0.0
    var li = 0
    var updated_TAT = 0.0
    do {
      arr = arr.filterNot(x => x(1) <= 0)
      q = arr(0)(1)
      for (i <- 0 to arr.size - 1) {
        if (tracker >= arr(i)(0)) {
          if (arr(i)(1) > q) { //if BT > quantum time
            arr(i)(1) -= q
            tracker = tracker + q
            for (j <- 0 to arr.size - 1) {
              if ((j != i) && (arr(j)(1) != 0))
                wt(j) += q
            }
          }
          else {
            for (j <- 0 to arr.size - 1) {
              if ((j != i) && (arr(j)(1) != 0)) {
                wt(j) += arr(i)(1)
              }
            }
            tracker = tracker + arr(i)(1)
            updated_TAT = tracker
            new_tat(li) = updated_TAT - arr_copy(i)(0)
            new_wt(li) = tracker - arr_copy(i)(1) - arr_copy(i)(0)
            li = li + 1
            arr(i)(1) = 0
          }
        }
      }
      sum = 0.0
      for (i <- 0 to arr.length - 1)
        sum = sum + arr(i)(1)
    } while (sum != 0)
    var avg_wt = 0.0
    var avg_tat = 0.0
    for (j <- 0 to n - 1)
      avg_wt += wt(j)
    for (j <- 0 to n - 1)
      avg_tat += new_tat(j)
    println("average waiting time= " + (avg_wt / n) + " Average turn around time= " + (avg_tat / n))
  }
}

try to go through these posts https://stackoverflow.com/questions/13337338/call-by-name-vs-call-by-value-in-scala-clarification-needed https://docs.scala-lang.org/tour/by-name-parameters.html — Irshad Babar, Mar 09 '19 at 04:06
Possible duplicate of [Call by name vs call by value in Scala, clarification needed](https://stackoverflow.com/questions/13337338/call-by-name-vs-call-by-value-in-scala-clarification-needed) — Paras Korat, Mar 09 '19 at 05:13

score 1 · Accepted Answer · answered Mar 09 '19 at 05:15

The problem is here:

var arr = data

arr is now a just a 2nd reference to the elements in data, so any modifications to arr (like arr(i)(1) = 0) are also modifications to data.

If you want to modify arr without changing data you'll need to make a deep copy. Something like this:

var arr = data.map(_.map(identity))

This is just one of the many, many, reasons why mutable variables (vars) and mutable data structures (Arrays) are bad, bad, bad. Good Scala code never (well, almost never) uses them.

@jwhv var arr = data.map(_.map(identity)) solved my problem – asif Mar 09 '19 at 07:32 — asif, Mar 09 '19 at 07:32

Passing same data to two or more methods in Scala

1 Answers1