Converting {Array {Float64,1}, 1} to {Float64,2} in Julia
My problem is similar to the previously described problem, with the difference that I do not enter numbers manually. So the accepted answer there doesn't work for me.
I want to convert a vector of Cartesian coordinates to polars:
function cart2pol(x0,
x1)
rho = sqrt(x0^2 + x1^2)
phi = atan2(x1, x0)
return [rho, phi]
end
@vectorize_2arg Number cart2pol
function cart2pol(x)
x1 = view(x,:,1)
x2 = view(x,:,2)
return cart2pol(x1, x2)
end
x = rand(5,2)
vcat(cart2pol(x))
The last command does not collect arrays for any reason, returning an output of type 5-element Array{Array{Float64,1},1}
. Any idea how to pass it to Array{Float64,2}
?
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If you look at the definition cat
(which is the main function for hcat
and vcat
), you can see that you can collect multiple arrays into one dimension 2 array:
cat(2, [1,2], [3,4], [5,6])
2×3 Array{Int64,2}:
1 3 5
2 4 6
This is basically what you want. The problem is that you have all of your output polar points in the array itself. cat
expects you to supply them as multiple arguments. Here ...
comes in.
...
is used to split one function argument into different arguments when used in the context of a function call.
Therefore you can write
cat(2, [[1,2], [3,4], [5,6]]...)
2×3 Array{Int64,2}:
1 3 5
2 4 6
In your situation, it works exactly the same (I changed yours x
to have dots in the columns):
x=rand(2,5) cat(2, cart2pol.(view(x,1,:),view(x,2,:))...) 2×5 Array{Float64,2}: 0.587301 0.622 0.928159 0.579749 0.227605 1.30672 1.52956 0.352177 0.710973 0.909746
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The function mapslices
can also do this by essentially converting the input strings:
julia> x = rand(5,2)
5×2 Array{Float64,2}:
0.458583 0.205246
0.285189 0.992547
0.947025 0.0853141
0.79599 0.67265
0.0273176 0.381066
julia> mapslices(row->cart2pol(row[1],row[2]), x, [2])
5×2 Array{Float64,2}:
0.502419 0.420827
1.03271 1.291
0.95086 0.0898439
1.04214 0.701612
0.382044 1.49923
The last argument defines the dimensions to work with; for example transfer [1]
will convert columns.
As an aside, I would recommend a stylistic change or two. First, it's good to render as we like, so if we're sticking to string representation then cart2pol
should accept an array of two elements (since it's returned). Then this challenge will only be mapslices(cart2pol, x, [2])
. Or if we are really trying to represent an array of arrays of coordinates, then the data can be an array of tuples [(x1,y1), (x2,y2), ...]
, or it cart2pol
can take and return a tuple. In any case cart2pol
, there would be no need to work with arrays, and partly because of this we have deprecated macros @vectorize_
.
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