What is the easiest way to determine if `list` con...

# announcements

[igor.wojda]

What is the easiest way to determine if list contains items with the same value (we don’t know what value it may be). Is there any operator or combination fo operators to achieve this ?
eg `

listOf("A", "A", "A")  //true
listOf("A", "A", "B")  //false
`

[edwardwongtl]

.all {}

[arekolek]

I understand he wants something like .toSet().size == 1

[igor.wojda]

Exactly @arekolek. Thanks

[ribesg]

I always have problems building entirely new collections just to check something. My algorithmics teacher would cry seeing this

[arekolek]

If you prefer to avoid creating the intermediary set, you could do for example .asSequence().zipWithNext().all { (a, b) -> a == b }

[ribesg]

Still creating a lot of stuff there, aren’t you?

[ribesg]

I would create and extension that does a simple while loop

[arekolek]

Only a Sequence object that uses the iterator

[ribesg]

It’s probably irrelevant with nowadays available power anyway, so I guess you should use the solution which is the shortest to both write and understand

[ribesg]

@arekolek .all does stuff too

[arekolek]

it iterates the Sequence, doesn’t create any objects

[ribesg]

The lambda itself is one

[arekolek]

inlined though

[ribesg]

I meant that the lambda compiled as a whole new class, and you’d use an instance of that class there

[ribesg]

I would create an extension function with a clear name which does a simple loop. Shorter than the sequence solution to write and understand and faster to understand than the set solution.

[Egor Trutenko]

But why would you do it, if all already does all the work 🤔

[arekolek]

I guess you could do it with just all like this all { first() == it }, is that what you mean?

[igor.wojda]

distinct may be also an option
listOf(1, 1, 1).distinct().size == 1 //true

[Egor Trutenko]

Oh, I just noticed that you don't know what value is inside the collection. I'm sorry, yes, all doesn't help

[arekolek]

I mean it kind of does, .run { all { first() == it } } makes more sense to me than the set or sequence ones

[Egor Trutenko]

Well, actually, you're right. For some weird reason I though that comparing each element to the first one is undeterministic

[dsavvinov]

Just bear in mind that all over an empty collection is always true, no matter what the passed predicate is (i.e. behaviour is different from the `toSet`/`distinct` approach)

See this demo: https://pl.kotl.in/r12sFGv2X

[igor.wojda]

Great tip @dsavvinov