Issue #16428 has been updated by gotoken (Kentaro Goto).


Recently I read similar topic again elsewhere. They pointed

* in most cases we have something to do on each duplicate element if any du=
plicate detected, e.g., reporting all duplicate elements as an error message
* `uniq?` looks slightly odd because we don't have `sort?` or `clear?` (uni=
q etymology: Perl funtion uniq. Originally Version 3 Unix command uniq.)

Though they make sense to me, but sometimes, in the case of back-of-the-env=
elope calculations, I just want to write code that just checks the array fo=
r duplicate elements, for example, to check whether a particular csv column=
 meets a unique constraint from the irb console as Keith gave as an example.

So instead, I suggest a set of three methods

* `#repeated` returns a new Array containing repeated elements. This may be=
 what we need.
* `#repeated?` returns `true` if there is a repeated element. This may be f=
aster than `! array.duplicate.empty?` because can return `true` immediately=
 when a repetition is detected.
* `#no_repeated?` returns the same to nagation of `#duplicate?`. This is wh=
at we want intuitively. And functionally identical to Kouhei's `uniq?`.

Here I chose word *repeated* instead of *duplicate* so as not to confuse it=
 with the meaning of `dup`.

----------------------------------------
Feature #16428: Add Array#uniq?, Enumerable#uniq?
https://bugs.ruby-lang.org/issues/16428#change-93281

* Author: kyanagi (Kouhei Yanagita)
* Status: Feedback
* Priority: Normal
----------------------------------------
I propose Array#uniq?.

I often need to check if an array have duplicate elements.

This method returns true if no duplicates are found in self, otherwise retu=
rns false.
If a block is given, it will use the return value of the block for comparis=
on.

This is equivalent to `array.uniq.size =3D=3D array.size`, but faster.

```
% ~/tmp/r/bin/ruby -rbenchmark/ips -e 'a =3D Array.new(100) { rand(1000) };=
 Benchmark.ips { |x| x.report("uniq") { a.uniq.size =3D=3D a.size }; x.repo=
rt("uniq?") { a.uniq? } }'
Warming up --------------------------------------
                uniq    25.765k i/100ms
               uniq?    76.544k i/100ms
Calculating -------------------------------------
                uniq    278.144k (=B1 4.1%) i/s -      1.391M in   5.010858s
               uniq?    981.868k (=B1 5.1%) i/s -      4.975M in   5.081611s
```

I think the name `uniq?` is natural because Array already has `uniq`.

patch: https://github.com/ruby/ruby/pull/2762



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