Filtering Values

Part of the Logic & Flow section of Coddy's Kotlin journey. Lesson 32 of 63.

filter keeps elements for which a predicate lambda returns true. It preserves their order and may return fewer elements or none. Chaining filter before map changes only the retained values.

Inside main:

println(listOf(-2, 0, 3, 4).filter { it > 0 }.map { it * 2 })

Only three and four pass the predicate; those values are then doubled.

filter decides membership with a Boolean predicate and preserves retained order.

Challenge

Medium

Complete positiveValues with parameters values: List<Int>. Return only strictly positive values, preserving their input order. Use filter.

Unless stricter bounds are stated above, collections contain at most 100 elements at each level, and integer arguments and integer collection values are between -1000 and 1000. Text supplied for parsing can include invalid or out-of-range representations as described.

Return a value of type List<Int>. Keep the supplied input/output code. It reads scalar arguments one per line; a list starts with its count followed by its elements, and a map starts with its entry count followed by each key and value. Nested lists repeat the count-and-elements format for each row. The supplied main prints the return value followed by one newline. Lists use Kotlin's standard bracketed format; print no additional labels.

Try it yourself

fun positiveValues(values: List<Int>): List<Int> {
    // Write your solution here.
    return emptyList()
}
fun main() {
    val valuesCount = readln().toInt()
    val values = mutableListOf<Int>()
    for (i0 in 0 until valuesCount) {
        val valuesItem = readln().toInt()
        values.add(valuesItem)
    }
    println(positiveValues(values))
}