Mapping vector of functions to vector of numbers?

New to Julia
1

Suppose I have a vector of functions, say f=[sin,cos] and I want to apply this element by element to a vector of numbers, say v=[2pi/3, pi/3] so that I get [sin(2pi/3), cos(pi/3)] – is there an elegant syntax for this?

1 Like
2

A comprehension is pretty elegant:

julia> f = [sin, cos]
2-element Array{Function,1}:
 sin
 cos

julia> v = [1, 2]
2-element Array{Int64,1}:
 1
 2

julia> [ff(vv) for (ff, vv) in zip(f, v)]
2-element Array{Float64,1}:
  0.8414709848078965
 -0.4161468365471424
3

Wouldn’t you want to get out four elements like

f=[sin,cos] 
v=[2pi/3, pi/3]

julia> [i(j) for i in f for j in v]
4-element Array{Float64,1}:
  0.8660254037844387
  0.8660254037844386
 -0.4999999999999998
  0.5000000000000001

?

(Not clear from OP I guess)

4

I would probably rely on an anonymous function that applies its first argument to its second argument, i.e.
(f,x) -> f(x).
This you can then map

map((f,x) -> f(x), [sin, cos], [2\pi/3, \pi/3])

or broadcast

((f,x) -> f(x)).([sin, cos], [2\pi/3, \pi/3])

or you can rely on list comprehesion as the others suggest

5 
f = [sin, cos]
w = [π/2, π]

julia> map.(f, w)
2-element Array{Float64,1}:
  1.0
 -1.0

julia> w .|> f
2-element Array{Float64,1}:
  1.0
 -1.0

(by the way, if you want good performance, you might want to check out FunctionWrappers.jl.)

10 Likes
6

The opposite might be easier, since it’s built into Julia:

f = [sin, cos]
w = [π/2, π]

julia> map(|>, w, f)
2-element Array{Float64,1}:
  1.0
 -1.0

julia> (|>).(w, f)
2-element Array{Float64,1}:
  1.0
 -1.0
2 Likes
7

Thanks for excellent answers. I’ll take a look into the various options – have to finish some other things at work first :-o .