How to best represent a list of points

Question

I have a set of points in 2D space that I'm representing as a rank 2 array: ``` points = [0 0; 0 1; 1 0] ``` It is a useful representation because it allows easy access to the x-, and y-components of the points. E.g. ``` plot(x=points[:,1], y=points[:,2]) ``` However, sometimes it would be better to view `points` as a list/set of points rather than as a matrix. For example, I need to check if a certain point (e.g. `[0 1]`) is an element of `points`. The straight-forward version does not work: ``` [0 1] in points # is false ``` Instead I have to manually expand `points` to a list of points: ``` [0 1] in [points[i,:] for i in 1:size(points)[1]] # is true ``` What is the proper julian way to define such a set of points, access components, and check for membership? Update: As @Jubobs suggested, I went ahead and defined my own type. As it turned out, I actually needed a vector, so I went ahead and called it `Vec2` instead of `Point`. ``` immutable Vec2{T<:Real} x :: T y :: T end Vec2{T<:Re…

Accepted Answer

I have a set of points in 2D space that I'm representing as a rank-2 array [...]

This calls for a set of pairs (tuples with two elements).

```
julia> myset = Set( [(0,0), (0,1), (1,0)] ) # define a set of tuples
Set{(Int64,Int64)}({(0,0),(1,0),(0,1)})

julia> in((0,0),myset)             # testing for membership is easy
true

julia> x = map (p -> p[1], myset)  # access to x values is easy with 'map'
3-element Array{Any,1}:
 0
 1
 0

julia> y = map (p -> p[2], myset)  # same thing with y values
3-element Array{Any,1}:
 0
 0
 1

julia> push!(myset,(3,2))          # adding an element to the set
Set{(Int64,Int64)}({(0,0),(1,0),(3,2),(0,1)})

julia> pop!(myset,(3,2))           # removing an element from the set
(3,2)

julia> myset
Set{(Int64,Int64)}({(0,0),(1,0),(0,1)})
```

How to best represent a list of points

Solution

Problem