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kotlinlang

If i have a list of pairs (to and from) and want to get the distinct sorted pairs that occur the most what would be the most functional way of doing it? So `[(1,2) , (3,4), (1,2)]` should return `[(1,2),(3,4)]`

Doesn't `pairs.distinct()` and then sorting by your criteria help?

I want it sorted by how many times it appears

```
listOf(1 to 2, 2 to 3, 1 to 2)
        .groupBy { it }
        .toList()
        .sortedBy { it.second.size }
        .flatMap { it.second } // Or if you want distinct then .map { it.first }
```

`listOf(1 to 2, 2 to 3, 1 to 2).groupingBy { it }.eachCount()` should be better performance-wise

That depends on the input size. Measure :slightly_smiling_face:

The list is expected to be 4000 pair elements 

Also what is the difference between groupBy and groupingBy

&gt; worth adding as sequence?
if these are all operations on the list, then it isn't.
&gt; Also what is the difference between groupBy and groupingBy
`groupBy` immediately produces a map of keys to lists of grouped values, and `groupingBy` allows to apply an aggregating operation to an each list on-the-fly, so the resulting map maps keys to the aggregation result of an each group.

&gt;all operations on a list
? When are they not? Do you mean things like map/sets? 

I mean if you're applying groupingBy directly on list, there's no gain in turning it to a sequence beforehand.