Hello, keen programmer! Are you ready for a sensational Scala venture? Today, our expedition encompasses the broad world of nested loops.

Nested loops serve as a pivotal mechanism to repeat an event or a collection of events. What sets them apart from ordinary loops is their unique ability to nest loops within other loops!

Our goal today is to hone our skill with simple nested loops in Scala. We'll start by understanding the basic syntax and control flow, delve into nested for and while loops, and conclude with common pitfalls to avoid when dealing with nested loops.

Before diving into nested loops, let's take a quick look back at for and while loops.

A for loop in Scala iterates over a ranged sequence:

Scala
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1for (i <- 1 to 5) {
2    println(i) // This prints numbers 1 to 5
3}

A while loop executes a block of code repeatedly as long as a given condition is true:

Scala
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1var count = 1
2while (count <= 5) {
3    println(count) // This also prints numbers 1 to 5
4    count += 1
5}

With our refreshed understanding of for and while loops, we can go deeper into the concept of nested loops. Put simply, a nested loop is a loop within a loop. For each iteration of the outer loop, the inner loop completes its entire cycle of iterations. Here's a basic nested loop in Scala:

Scala
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1for(outer <- 1 to 2){
2    for(inner <- 1 to 3){
3        println(s"Outer:$outer Inner:$inner")
4    }
5}
6
7/*
8This code provides the following output:
9Outer:1 Inner:1
10Outer:1 Inner:2
11Outer:1 Inner:3
12Outer:2 Inner:1
13Outer:2 Inner:2
14Outer:2 Inner:3
15*/

Nested for loops execute all their iterations within each cycle of the outer loop, making them highly effective for managing tasks such as processing two variables in a systematic way.

Scala
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1for(row <- 1 to 3) {
2    for(col <- 1 to 4) {
3        print("* ")
4    }
5    println() // jump to next line after each row
6}
7
8/*
9This code provides the following output:
10* * * * 
11* * * * 
12* * * * 
13*/

Another interesting Scala way of having nested loops is combining the two loops in a single line. This can make the code more concise:

Scala
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1for (i <- 1 to 2; j <- 1 to 2) {
2    println(s"i: $i, j: $j")
3}
4
5/*
6This code provides the following output:
7i: 1, j: 1
8i: 1, j: 2
9i: 2, j: 1
10i: 2, j: 2
11*/

By using this concise form, you achieve the same functionality as the traditional nested loops but with more compact and readable code. This technique is particularly useful when you need to iterate over combinations of two ranges. Here, for every combination of i and j, the values are printed on the same line.

Like for loops, there is also potential for nesting while loops too. However, remember to manage the control variable within the loop carefully to avoid creating infinite loops. Here's an example of a nested while loop:

Scala
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1var row = 1
2while (row <= 3) {
3    var col = 1
4    while (col <= 4) {
5        print("* ")
6        col += 1
7    }
8    println()
9    row += 1
10}
11
12/*
13This code provides the following output:
14* * * * 
15* * * * 
16* * * * 
17*/

Infinite loops, especially with nested while loops, are a common mistake to avoid. To prevent this, always ensure the values of the loop variables are correctly managed within the loop.

Scala
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1var row = 1
2while (row <= 3) {
3    var col = 1
4    while (col <= 4) {
5        print("* ")
6        // col += 1 // Not including this line will cause an infinite loop
7    }
8    println()
9    row += 1
10}

Hooray! Today, you navigated through simple nested loops in Scala. Now, armed with nested loops, you're prepared to deal with a more structured looping mechanism. Maintain your enthusiasm—our upcoming practice challenges will help you cement your understanding and apply your newly-acquired knowledge. Each completed task brings you closer to fluency in Scala. So, brace yourself for our intensified learning journey into Scala!