Kotlin HashMap contain keys using an array - hashmap

Question

Is there any way to check a HashMap if it contains a certain set of keys which keys are given in an array. When I try something like the code below it returns false.
map.containsKey(arrayOf("2018-01-16"))
If I try the following code it works but I need to check for the keys and the numbers of keys that I need to search is not fixed.
map.containsKey("2018-01-16")

Answer 1

You can start from the keys themselves, and use the all function from the standard library:
val map = hashMapOf(...)
val keys = arrayOf("2018-01-16", "2018-01-17", "2018-01-18")
val containsAllKeys = keys.all { map.containsKey(it) }
If you do this a lot and want to have this functionality on the Map type, you can always add it as an extension:
fun <K, V> Map<K, V>.containsKeys(keys: Array<K>) = keys.all { this.containsKey(it) }
val containsAllKeys = map.containsKeys(arrayOf("2018-01-16", "2018-01-17"))
You might also want to overload the extension with another function that takes an Iterable<K> as the parameter.

Answer 2

Map has keys collection, which as every collection implements containsAll method, so you can use it to check whether the keys collection contains all of the keys:
map.keys.containsAll(keysArray.asList())

Answer 3

You could use ArrayList<T> as a key, since it's equals is different as the Array<T> one. Let's see this test:
class ExampleUnitTest {
#Test
fun arrayAsKeyTest() {
val hashMapOne = HashMap<Array<String>, Int>()
val stringKeysOne1 = arrayOf("a", "b")
hashMapOne.set(stringKeysOne1, 2)
val stringKeysOne2 = arrayOf("a", "b")
// NOT MATCH! As stringKeysOne1 == stringKeysOne2 is false
assertFalse(hashMapOne.containsKey(stringKeysOne2)) // NOT MATCH
val hashMapTwo = HashMap<ArrayList<String>, Int>()
val stringKeysTwo1 = arrayListOf("a", "b")
hashMapTwo.set(stringKeysTwo1, 2)
val stringKeysTwo2 = arrayListOf("a", "b")
// MATCH! As stringKeysTwo1 == stringKeysTwo2 is true (although stringKeysTwo1 === stringKeysTwo2 is false)
assertTrue(hashMapTwo.containsKey(stringKeysTwo2)) // MATCH
}
}