Welcome! Today, we'll explore Data Projection Techniques in Kotlin. Data projection is akin to using a special light to make diamonds shine brighter amidst other gems, aiding in their identification.

This lesson will equip you with the concepts of data projection, its implementation using Kotlin's collection operations, and how to integrate it with filtering. Let's forge ahead!

Data projection involves applying a function to elements of a data stream, resulting in a reshaped view. A common instance of data projection is selecting specific fields from data collections.

In Kotlin, you can use named functions for data projection with the map method. Here’s an example of finding each number's square in a list using a named function:

Kotlin
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1fun square(n: Int): Int {
2    return n * n  // function to get a number's square
3}
4
5fun main() {
6    val numbers = listOf(1, 2, 3, 4, 5)  // our data stream
7    
8    // map applies the square function to each number in the list
9    val squaredNumbers = numbers.map(::square)
10    
11    println(squaredNumbers)  // prints: [1, 4, 9, 16, 25]
12}

1. The square function is defined to compute the square of a given number:

   • Takes an integer input and returns its square value
   • Serves as a reusable transformation function

2. The map method applies this function to each element:

   • Iterates through the entire list
   • Transforms each element using the provided function
   • Creates a new list with transformed values

3. The ::square syntax creates a function reference:

   • Converts the named function into a callable reference
   • Allows passing the function as an argument to map

4. The result is stored in squaredNumbers

For more complex operations on data streams, Kotlin employs lambda expressions. Let's convert a list of sentences to lowercase:

Kotlin
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1fun main() {
2    val sentences = listOf("HELLO WORLD", "KOTLIN IS FUN", "I LIKE PROGRAMMING")  // our data stream
3    
4    // map applies the lambda function to transform each sentence to lowercase
5    val lowerSentences = sentences.map { sentence -> sentence.lowercase() }
6    
7    println(lowerSentences)  // prints: [hello world, kotlin is fun, i like programming]
8}

Kotlin seamlessly combines projection and filtering. Let's transform sentences containing "KOTLIN" to lowercase while ignoring others:

Kotlin
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1fun main() {
2    val sentences = listOf("HELLO WORLD", "KOTLIN IS FUN", "I LIKE PROGRAMMING")  // our data stream
3    
4    // filter selects sentences containing 'KOTLIN'
5    val filteredSentences = sentences.filter { sentence -> sentence.contains("KOTLIN") }
6    
7    // map applies the lambda function to convert filtered sentences to lowercase
8    val lowerFilteredSentences = filteredSentences.map { sentence -> sentence.lowercase() }
9    
10    println(lowerFilteredSentences)  // prints: [kotlin is fun]
11}

By creating a DataProjector class, we'll encapsulate our projections for reusable, cleaner code in Kotlin:

Kotlin
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1class DataProjector(private val data: List<String>) {
2    
3    fun filterAndProject(filterFunc: (String) -> Boolean, projectFunc: (String) -> String): List<String> {
4        return data.filter(filterFunc).map(projectFunc)
5    }
6}
7
8fun main() {
9    val sentences = listOf("HELLO WORLD", "KOTLIN IS FUN", "I LIKE PROGRAMMING")  // our data stream
10    val projector = DataProjector(sentences)
11    
12    // Apply filterAndProject to filter sentences containing 'KOTLIN' and convert them to lowercase
13    val lowerFilteredSentences = projector.filterAndProject(
14        { sentence -> sentence.contains("KOTLIN") },
15        { sentence -> sentence.lowercase() }
16    )
17    
18    println(lowerFilteredSentences)  // prints: [kotlin is fun]
19}

Awesome! You've conquered Data Projection Techniques in Kotlin! You've delved into data projection, utilized map, and seamlessly integrated projection with filtering using Kotlin's collections.

Remember our treasure box! This knowledge is your treasure box key, unlocking data manipulation aspects like raw data cleaning or transformations for various applications. Now, revisit these concepts with practice exercises for mastery. Happy coding!