fun <T, K, M : MutableMap<in K, Int>> Grouping<T, K>.eachCountTo( destination: M ): M
Platform and version requirements: Kotlin 1.1
Groups elements from the Grouping source by key and counts elements in each group to the given destination map.
If the destination map already has a value corresponding to the key of some group, that value is used as an initial value of the counter for that group.
Return the destination map associating the key of each group with the count of elements in the group.
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Licensed under the Apache License, Version 2.0.
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/each-count-to.html