Scala: Haar Wavelet Transform - scala

Question

I am trying to implement Haar Wavelet Transform in Scala. I am using this Python Code for reference Github Link to Python implementation of HWT
I am also giving here my Scala code version. I am new to Scala so forgive me for not-so-good-code.
/**
* Created by vipul vaibhaw on 1/11/2017.
*/
import scala.collection.mutable.{ListBuffer, MutableList,ArrayBuffer}
object HaarWavelet {
def main(args: Array[String]): Unit = {
var samples = ListBuffer(
ListBuffer(1,4),
ListBuffer(6,1),
ListBuffer(0,2,4,6,7,7,7,7),
ListBuffer(1,2,3,4),
ListBuffer(7,5,1,6,3,0,2,4),
ListBuffer(3,2,3,7,5,5,1,1,0,2,5,1,2,0,1,2,0,2,1,0,0,2,1,2,0,2,1,0,0,2,1,2)
)
for (i <- 0 to samples.length){
var ubound = samples(i).max+1
var length = samples(i).length
var deltas1 = encode(samples(i), ubound)
var deltas = deltas1._1
var avg = deltas1._2
println( "Input: %s, boundary = %s, length = %s" format(samples(i), ubound, length))
println( "Haar output:%s, average = %s" format(deltas, avg))
println("Decoded: %s" format(decode(deltas, avg, ubound)))
}
}
def wrap(value:Int, ubound:Int):Int = {
(value+ubound)%ubound
}
def encode(lst1:ListBuffer[Int], ubound:Int):(ListBuffer[Int],Int)={
//var lst = ListBuffer[Int]()
//lst1.foreach(x=>lst+=x)
var lst = lst1
var deltas = new ListBuffer[Int]()
var avg = 0
while (lst.length>=2) {
var avgs = new ListBuffer[Int]()
while (lst.nonEmpty) {
// getting first two element from the list and removing them
val a = lst.head
lst -= 1 // removing index 0 element from the list
val b = lst.head
lst -= 1 // removing index 0 element from the list
if (a<=b) {
avg = (a + b)/2
}
else{
avg = (a+b+ubound)/2
}
var delta = wrap(b-a,ubound)
avgs += avg
deltas += delta
}
lst = avgs
}
(deltas, avg%ubound)
}
def decode(deltas:ListBuffer[Int],avg:Int,ubound:Int):ListBuffer[Int]={
var avgs = ListBuffer[Int](avg)
var l = 1
while(deltas.nonEmpty){
for(i <- 0 to l ){
val delta = deltas.last
deltas -= -1
val avg = avgs.last
avgs -= -1
val a = wrap(math.ceil(avg-delta/2.0).toInt,ubound)
val b = wrap(math.ceil(avg+delta/2.0).toInt,ubound)
}
l*=2
}
avgs
}
def is_pow2(n:Int):Boolean={
(n & -n) == n
}
}
But Code gets stuck at "var deltas1 = encode(samples(i), ubound)" and doesn't give any output. How can I improve my implementation? Thanks in advance!

Answer 1

Your error is on this line:
lst -= 1 // removing index 0 element from the list.
This doesn't remove index 0 from the list. It removes the element 1 (if it exists). This means that the list never becomes empty. The while-loop while (lst.nonEmpty) will therefore never terminate.
To remove the first element of the list, simply use lst.remove(0).