I played with it a bit more and am seeing some unexpected behavior. If you
add a mutable element, change it, and then add another equal one, the set
gets two elements. But if you don't mutate the element, it stays at one.
julia> s = Set{Vector{Int}}()
Set{Array{Int64,1}}()
julia> el = [1,2,3]; push!(s, el)
Set([[1,2,3]])
julia> push!(s, [1,2,3]) #Pushing a new array object, but the length stays
at 1.
Set([[1,2,3]])
julia> s = Set{Vector{Int}}()
Set{Array{Int64,1}}()
julia> el = [1,2,3]; push!(s, el)
Set([[1,2,3]])
julia> el[1] = 10; @show s; #Mutate the set element from the outside
s = Set([[10,2,3]])
julia> push!(s, [10,2,3])
Set([[10,2,3],[10,2,3]])
julia> length(s)
2
julia> els = collect(s); els[1] == els[2]
true
Is something buggy going on here?
On Tuesday, December 15, 2015 at 10:57:31 AM UTC-5, Josh Langsfeld wrote:
>
> It's not array equality that's the issue here. Arrays with the same
> elements are '==' (but not '==='). If you manually test pushing the same
> array to a Set you'll see it works fine.
>
> Jan, what happened is that your 'santa' function modifies and returns the
> same array that was passed in instead of creating a new one. So the only
> array that ever gets created is the first 'start = [0 0]' and it just gets
> continually modified, both in the santa function and in the set. Switching
> to a tuple works because you are forced to create a new tuple to change one
> of the elements.
>
> On Tuesday, December 15, 2015 at 3:32:40 AM UTC-5, Tomas Lycken wrote:
>>
>> Probably because the arrays will not be equal even if their contents are
>> equal (this is true of most mutable types in Julia).
>>
>> If you try representing a position as a tuple `(0,0)` instead of as an
>> array `[0,0]`, you'll find that it works as expected.
>>
>> // T
>>
>> On Tuesday, December 15, 2015 at 8:28:36 AM UTC+1, Jan Strube wrote:
>>>
>>> That's not a problem at all. In fact that's the very reason why I'm
>>> using a Set in the first place.
>>>
>>> My question is: Why is the number of entries in the set different when I
>>> add Arrays vs. adding ASCIIStrings?
>>>
>>>
>>> On Monday, December 14, 2015 at 10:57:57 PM UTC-8, [email protected]
>>> wrote:
>>>>
>>>> I think your problem is that Sets cannot contain duplicate entries, so
>>>> if Santa ever passes the same point twice it won't be added.
>>>>
>>>> Cheers
>>>> Lex
>>>>
>>>> On Tuesday, December 15, 2015 at 4:23:19 PM UTC+10, Jan Strube wrote:
>>>>>
>>>>> I'm trying to learn a bit more Julia by solving the puzzles over on
>>>>> http://adventofcode.com
>>>>> On day 3, the problem is to follow a number of directions and figure
>>>>> out how many new places you end up.
>>>>> http://adventofcode.com/day/3
>>>>>
>>>>> I thought I can solve this simply by defining a set of [x y]
>>>>> positions, each time adding a new grid position to the set, so I'd end up
>>>>> with a Set{ Array{Int64,2}} of the right length.
>>>>> However, this doesn't work as expected. I get the wrong number (it's
>>>>> too low).
>>>>>
>>>>> Wrapping each grid position into a string() call, however, gives me
>>>>> the right answer.
>>>>> The explanation is a bit convoluted. To avoid spoilers I've put the
>>>>> code up at https://gist.github.com/jstrube/3d54e15f7d051b72032b
>>>>>
>>>>> I don't quite understand this. Is this expected?
>>>>>
>>>>>
