# Merge a list of maps

**URL:** <https://discuss.kotlinlang.org/t/merge-a-list-of-maps/22375>\
**Category:** Support\
**Created:** [July 10, 2021, 11:30am UTC](https://discuss.kotlinlang.org/t/merge-a-list-of-maps/22375 "2021-07-10T11:30:11Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Psijic](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/psijic/32/2227_2.png) [@Psijic](https://discuss.kotlinlang.org/u/Psijic)\
**Post date:** [July 10, 2021, 11:30am UTC](https://discuss.kotlinlang.org/t/merge-a-list-of-maps/22375/1 "2021-07-10T11:30:11Z")

</div>

Hello, I’m trying to understand some Kotlin data mapping functions (which are a lot of them and there is a need to read a separate book). The case is next: I need to flat `List<HashMap<String, List<String>>>` and merge all the values. So, I found a solution:

```auto
    @Test
    fun foldMap() {
        val list = listOf(
            hashMapOf("A" to listOf("a1", "a2"), "B" to listOf("b1", "b2")),
            hashMapOf("A" to listOf("a11", "a21"), "C" to listOf("c11", "c21")),
            hashMapOf("C" to listOf("c12", "c22"))
        )

        val map = list.fold(hashMapOf<String, List<String>>()) { acc, curr ->
            curr.forEach { entry ->
                acc.merge(entry.key, entry.value) { new, old -> new + old }
            }
            acc
        }

        assertEquals("{A=[a1, a2, a11, a21], B=[b1, b2], C=[c11, c21, c12, c22]}", map.toString())
    }

```

Can the `map` calculation be shorter?