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Julia allows me to do elementwise binary operators on arrays/matrices with .:
[1 2 3] .+ [3 2 1]
[1 2 3] .> [3 2 1]
Is there a standard way to apply an arbitrary function f elementwise to a pair of arrays?
631
It is just a variable name. R variables names can consist of alphanumerics and dot (.)
In technical language, this is called an ellipsis. And it means that the function is designed to take any number of named or unnamed arguments. By the way, the ellipsis is not a specialty of R. Other programming languages have the same or a similar concept.
def is the keyword for defining a function. The function name is followed by parameter(s) in (). The colon : signals the start of the function body, which is marked by indentation. Inside the function body, the return statement determines the value to be returned.
If you just want to apply a binary function to each pair of values from two lists, you can use map:
f(x,y) = 2x - y^2
julia> map(f, [1, 2, 3], [3, 2, 1])
3-element Array{Int64,1}:
-7
0
5
The .+ and .> operators also have the additional behavior that singleton dimensions are broadcast, like so:
julia> [1, 2, 3] .+ [-1 -2 -3]
3x3 Array{Int64,2}:
0 -1 -2
1 0 -1
2 1 0
julia> rand(3,4) .+ [1, 2, 3]
3x4 Array{Float64,2}:
1.73798 1.84132 1.12923 1.30192
2.10961 2.17835 2.52779 2.3028
3.16457 3.04659 3.67604 3.08869
julia> rand(3,4) .+ [1 2 3 4]
3x4 Array{Float64,2}:
1.40294 2.31384 3.34001 4.60027
1.13289 2.99275 3.50606 4.51049
1.31486 2.7585 3.64655 4.59647
If you also want this kind of behavior, you can use the broadcast function:
julia> broadcast(f, [1 2 3], [3, 2, 1])
3x3 Array{Int64,2}:
-7 -5 -3
-2 0 2
1 3 5
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