s1monw1

fun <T> countOccurrences(values: Collection<T>): Map<T, Int> =
    mutableMapOf<T, Int>().withDefault { 0 }.apply {
        for (e in values) {
            put(e, getValue(e) + 1)
        }
    }

s1monw1

fun <T> countOccurrences(values: Collection<T>): Map<T, Int> {
    val countMap = mutableMapOf<T, Int>().withDefault { 0 }
    for (e in values) {
        countMap[e] = countMap.getValue(e) + 1
    }
    return countMap
}

s1monw1

fun <K, V> MutableMap<K, V>.withDefault(defaultValue: (key: K) -> V): MutableMap<K, V>

s1monw1

fun <T> countOccurrences(values: Collection<T>): Map<T, Int> {
    val countMap = mutableMapOf<T, Int>()
    for (e in values) {
        countMap.putIfAbsent(e, 0)
        // getValue, as an alternative to index operator, 
        // makes sure a non-nullable type is returned
        countMap[e] = countMap.getValue(e) + 1
    }
    return countMap
}

s1monw1

fun <T> countOccurrences(values: Collection<T>): Map<T, Int> {
    val countMap = mutableMapOf<T, Int>()
    for (e in values) {
        val current = countMap[e]
        if (current == null) countMap[e] = 1 
        else countMap[e] = current + 1
    }
    return countMap
}

s1monw1

fun <T> countOccurrences(values: Collection<T>): Map<T, Int>

s1monw1

from collections import defaultdict 
d = defaultdict(int)
print(d["someKey"]) // prints 0

s1monw1

from collections import defaultdict 

data = [('red', 1), ('blue', 2), ('red', 3), ('blue', 4), ('red', 1), ('blue', 4)]

d = defaultdict(set)
for k, v in data:
    d[k].add(v)
    
print(d.items()) # dict_items([('red', {1, 3}), ('blue', {2, 4})])

s1monw1

inline fun <T, R> with(receiver: T, block: T.() -> R): R

s1monw1

inline fun  T.apply(block: T.() -> Unit): T