Bounds Error?

General Usage
,
1

I am trying to run the following code:

u_vect = rand(5,2)   
for i in eachindex(u_vect)
    println(i)
    a = u_vect[i,2] 
end

And get the error: “BoundsError: attempt to access 5×2 Matrix{Float64} at index [6, 2].” Why does my 5x2 vector have 6 index positions? I know that arrays are considered one dimensional, but that still doesn’t explain the error?

2

eachindex goes over every index of the matrix, since your matrix has 10 entries in total, it goes from 1 to 10:

julia> eachindex(u_vect)
Base.OneTo(10)

If you only want to iterate over the first dimension of the matrix, you’ll need to use the axes function, with the desired dimension:

julia> axes(u_vect,1)
Base.OneTo(5)

julia> axes(u_vect,2)
Base.OneTo(2)
2 Likes
3

eachindex(u_vect) gives you the linear indices of every element in the matrix:

julia> eachindex(u_vect)
Base.OneTo(10)

So by doing u_vect[i, 2], you’re trying to access u_vect[1, 2], u_vect[2, 2], ..., u_vect[10, 2], which doesn’t work (it errors as soon as you get to u_vect[6, 2]).

If you’re using eachindex, then you want to index with just i, as in:

for i in eachindex(u_vect)
  a = u_vect[i]
  ...
end

or if you just want to iterate over the indices in the first dimension, then you want axes:

for i in axes(u_vect, 1)
  a = u_vect[i, 2]
  ...
end
4 Likes
4

thank you so much!

5

thank you!!!