Welcome to another lesson where we'll explore the fundamental technique of reading files line-by-line using Scala's os-lib library. In many real-world applications, especially those dealing with large files such as logs or continuous data streams, processing data line-by-line is vital for effective data management. By the end of this lesson, you'll be well-equipped to read and process file data line-by-line using Scala.

To read a file line-by-line in Scala, you can utilize the os.read.lines method to obtain a collection of lines and then iterate over each line using the foreach method. Let's examine this process in action:

Scala
Copy to clipboard
1import os._
2
3@main def main() =
4  // Specify the file path
5  val filePath = os.pwd / "data.txt"
6
7  // Read all lines from the file
8  val lines = os.read.lines(filePath)
9
10  // Iterate through each line and output it
11  lines.foreach(println)

In this example, os.read.lines(filePath) reads all the lines from data.txt and returns them as a collection. We then print each line to the console using the foreach method.

Imagine needing to process a set of numbers stored in a file — reading each integer and calculating their sum. This task can be easily accomplished using Scala’s os-lib.

Assume numbers.txt contains:

Plain text
Copy to clipboard
110
220
330
440

Here's some Scala code to read integers from this file and calculate their sum:

Scala
Copy to clipboard
1import os._
2
3@main def main() =
4  // Specify the file path
5  val filePath = os.pwd / "numbers.txt"
6  
7  // Read all lines from the file
8  val lines = os.read.lines(filePath)
9
10  // Initialize a variable to hold the sum of integers from the file
11  var totalSum = 0
12
13  // Iterate through each line, convert to integer, and add to totalSum
14  lines.foreach { line =>
15    try {
16      val number = line.toInt
17      totalSum += number // Add the integer to totalSum
18    } catch {
19      case _: NumberFormatException => 
20        println(s"Invalid number format in line: $line")
21    }
22  }
23  
24  // Display the total sum
25  println(s"The sum of the numbers is: $totalSum")

• Reading Numbers: Each line is parsed to an integer using toInt, which converts strings to integers.
• Calculating Sum: The integers are summed in the totalSum variable.

Running this code will display the total sum of the numbers:

Plain text
Copy to clipboard
1The sum of the numbers is: 100

In this lesson, you've acquired the skills to read a text file line-by-line using Scala — a crucial technique for processing large datasets efficiently. You've learned how to manage file I/O operations with os-lib, and how to handle each line of text data effectively in Scala applications. You're now well-prepared to tackle practice exercises applying these concepts and to further explore parsing techniques in future lessons. Continue building on these skills and enjoy the Scala journey!