Kotlin Koans 21 Filter; map

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目次

Filter; map (Playground)

Description

Implement extension functions Shop.getCitiesCustomersAreFrom() and Shop.getCustomersFrom() using functions map and filter.

map と filter を使用して、拡張関数 Shop.getCitiesCustomersAreFrom() および Shop.getCustomersFrom() を実装してください。

val numbers = listOf(1, -1, 2)
numbers.filter { it > 0 } == listOf(1, 2)
numbers.map { it * it } == listOf(1, 1, 4)

Code 

// Return the set of cities the customers are from
fun Shop.getCitiesCustomersAreFrom(): Set<City> = customers.map { it.city }.toSet()

// Return a list of the customers who live in the given city
fun Shop.getCustomersFrom(city: City): List<Customer> = customers.filter { it.city == city }

Memo

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