Anonymous function as argument

New to Julia
1

Why is common practice to use anonymous funtions where a normal function could be used instead? I’m specilly thinking when using it as an argument of another function. For example:

plot(0:0.1:2π, x -> sin(x))

I’ve seen code like that a lot but I don’t know why since

plot(0:0.1:2π, sin)

works perfectly fine.

2

I haven’t seen that. Can you link to an example?

1 Like
3

Basically is the same as my MWE but here is this example from a Chaos course:

function analisis_grafico(f, x0::Float64, n::Int, domx=0.0:1/128:1.0)
    #Graficamos x->F(x) y x->x
    Plt1 = plot(domx, x->f(x),
        xaxis=("x", (domx[1], domx[end])),
        yaxis=("f(x)"),
        color=:blue, legend=false, grid=false)

    plot!(Plt1,
        domx, identity, color=:blue, linestyle=:dash)

    #Se grafican los iterados
    analisis_grafico!(Plt1, f, x0, n, domx)
    return Plt1
end

I’ve seen this in other contexts but I don’t remember them right now.

4

I’d guess they just weren’t thinking about it.

5

Yeah, there’s no particular reason to do that, and it’s certainly not necessary. I’d guess that you might occasionally see it in a context where someone is trying to show more generally how an anonymous function /could/ be used, and they’ve just unintentionally chosen an example that could also be written without one.

1 Like
6

In that particular case that is not needed, but if they wanted to use an additional parameter for the function they could have done something like:

f(x,a) = a*x
function analisis_grafico(f, x0::Float64, n::Int, domx=0.0:1/128:1.0)
    a = 5.0
    Plt1 = plot(domx, x->f(x,a),
...

because the plot function is expecting a function with one variable, but you want to pass to it a function with two, one being a fixed parameter.

7 Likes
7

I have used something similar when the function f takes keyword arguments that I want to move away from the default values.

8

:thinking:

9

Yeah, I was also thinking that it would be necesary in the following example:

plot(0:0.1:2π, x -> sin(x^2))
10

Do you have an example?

11 
function f(x; exponent=2)
    sin(x^exponent)
end

plot(0:0.1:2π, x -> f(x; exponent=3))
1 Like
12

Got it, thanks. (:

13

Thank you all for your replies. In the example I gave, there is no need to use an anonymous function but it is necessary to reduce the number of arguments of a function.

1 Like