$.uniq doesn't retain order

[djones]

println(",".join($.uniq(["Stockholm", "Stockholm", "SE"])))

Outputs

SE,Stockholm

It should output

Stockholm,SE

[ankurp]

The order is not guaranteed as few things can happen. If order is important then either it is sorted and returned, or it is returned in the order it was passed.

[djones]

it is returned in the order it was passed.

This is what I would expect to happen but that doesn't currently happen.

Order isn't kept for $.uniq but other methods such as $.compact do return things in the order they are passed. So I guess I was expecting $.uniq to do the same.

If you think $.uniq shouldn't keep the order then this issue becomes a feature request for a method that provides $.uniq returning items in the same order they were provided.

[djones]

Also thanks for a great library. It covers off so many things that should be standard in Swift.

[ankurp]

Yes adding it as an option makes sense as underneath it is using dictionary keys and returning that which are uniq but the order is ignored for speed.

[ankurp]

Now the other thing to figure out is what is the order if there are duplicate values as such [Stockholm, SE, Stockholm]

[ankurp]

Should it be [Stockholm, SE] or [SE, Stockholm]. The question is should we pick the last uniq value and its order or pick the first and use that order.

[djones]

I think [Stockholm, SE]. It makes sense to me to iterate through the array in order, accepting return values if they are unique and then discarding anything that comes up that isn't uniq.

So $.uniq([1,2,3,1,4]) outputs [1,2,3,4]

You were talking about performance which is great. Would the optional be something like this:

$.uniq([1,2,3,1,4], preserveOrder: true)

The question is would order preservation be turned on or off by default? I'd be interested to know what you think, but my opinion is it would be better to keep Dollar.swift accurate by default, not tripping people up but have the option of disabling order preservation for speed.

Array's in Swift by default preserve order and so this is why I raised this issue because I ran my array through $.uniq and suddenly it was not in order!

Are there other instances where you've had to decide on speed vs accuracy? If so which did you pick?

[djones]

Thanks heaps @ankurp!

[ankurp]

No problem.