Collection chains in Kotlin

filter, map and friends read left to right and never mutate.

fun main() {
    val legsKm = listOf(8.4, 11.2, 6.9, 14.5, 9.1)

    // Chains read left to right; each call returns a new list.
    val hardDays = legsKm.filter { it > 9.0 }
    println("$hardDays add up to ${hardDays.sum()} km")

    val paces = legsKm.map { km -> (60 * km / 4.5).toInt() }
    println("Minutes per leg: $paces")

    println("Total: ${legsKm.sumOf { it }} km in ${legsKm.count()} days")
    println("Any rest day? ${legsKm.any { it < 7.0 }}")
}

How it works

filter { it > 9.0 } keeps the hard days; sum folds them.
map transforms each leg into minutes with a named lambda parameter.
sumOf, count and any answer the usual questions in one call each.

Keywords and builtins used here

fun
it
main
val

The run, in numbers

Lines: 13
Characters to type: 432
Tokens: 121
Three-star pace: 70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 104 seconds.

Type this snippet

Step 2 of 3 in Collections, step 11 of 27 in Language basics.

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