BoundsError: attempt to access 0-element Array{Any,1} at index [1]

General Usage
1

Hello, this is my code:

distvec = []
for indm = 1:M
    global distvec
    distvec[indm] = -(-Nvec[1]* px[indm]- Nvec[2]* py[indm]- Nvec[3]* pz[indm])/sqrt(Nvec[1]^2+Nvec[2]^2+Nvec[3]^2) 
end

The error I get:

BoundsError: attempt to access 0-element Array{Any,1} at index [1]

How do I solve this issue?

Thank you!

2

You want to preallocate distvec to the correct length, e.g. if your numbers are floats do

distvec = zeros(M)

or Array{Float64, 1}(undef, M) if you want to leave the elements uninitialized.

3 Likes
3

The line distvec = [] declares an empty array, so you cannot do distvec[1] = 0.1. You could do push!(distvec, 0.1), but it’s better to pre-allocate the array with the correct size.

Also, avoid globals as much as possible. If you put this code in a function you don’t need a global:

function f(M, Nvec, px, py, pz)
    # Preallocate an array full of 0.0 (write e.g. zeros(Int, M) to choose a type different from Float64)
    distvec = zeros(M)
    for indm = 1:M
        distvec[indm] = -(-Nvec[1]* px[indm]- Nvec[2]* py[indm]- Nvec[3]* pz[indm])/sqrt(Nvec[1]^2+Nvec[2]^2+Nvec[3]^2) 
    end
    return distvec
end

f(5, [1,2,3], 1:5, 1:5, 1:5)

If you don’t want to preallocate, at least create an array with a specific type, e.g. distvec = Float64[] instead of distvec = [].

You can also use array comprehension:

M = 5
Nvec = [1,2,3]
px = py = pz = 1:M

distvec = [-(-Nvec[1]*px[indm] - Nvec[2]*py[indm] - Nvec[3]*pz[indm]) / norm(Nvec)
           for indm in 1:M]
3 Likes
4

Thank you all!