What wrong with this Scala loop in reading files - scala

Question

I am using Scala to read data from 2 CSV files and for each line from the first file, I want to scan all line from the second CSV file to do some calculating.
This is my code
object CSVProcess extends App {
val dataMatlab = io.Source.fromFile("./data/data_matlab1.csv")
val matchDataMatlab = io.Source.fromFile("./data/match_data_matlab1.csv")
for ((line, count) <- dataMatlab.getLines.zipWithIndex) {
for ((line1, count1) <- matchDataMatlab.getLines.zipWithIndex) {
println(s"count count1 ${count} ${count1}")
}
}
dataMatlab.close
matchDataMatlab.close
However, the output does not like what I expect, the loop stops when the first line of the first CSV file scans all lines of the second one.
For example, in the CSV 1, There are 3 lines
1,1
2,2
3,3
In the CSV 2, It has3 lines
1,1,1
2,2,2
3,3,3
But the output is
count count1 0 0
count count1 0 1
count count1 0 2
The output should be
count count1 0 0
count count1 0 1
count count1 0 2
count count1 1 0
count count1 1 1
count count1 1 2
count count1 2 0
count count1 2 1
count count1 2 2
.
Could someone detect the problem of my code

Answer 1

The problem is io.Source.fromFiles("path").getLines gives you a iterator and Iterators are like socket buffers meaning that once you read a data out of it, there would be no data left.
official scala documentation explains as
An iterator is not a collection, but rather a way to access the elements of a collection one by one. The two basic operations on an iterator it are next and hasNext. A call to it.next() will return the next element of the iterator and advance the state of the iterator. Calling next again on the same iterator will then yield the element one beyond the one returned previously...
The solution would be to convert the iterators to any of the traversables. Here I have converted to List for persistance.
val dataMatlab = io.Source.fromFile("./data/data_matlab1.csv").getLines().toList
val matchDataMatlab = io.Source.fromFile("./data/match_data_matlab1.csv").getLines().toList
for ((line, count) <- dataMatlab.zipWithIndex) {
for ((line1, count1) <- matchDataMatlab.zipWithIndex) {
println(s"count count1 ${count} ${count1}")
}
}
now you should get the expected output
I hope the explanation is clear enough and helpful