Inclusivity of Julia ranges

user_5323423 0
Viewed 105

I hate that ranges include the end. Here is an example where I've deliberately removed the end of the range.

N = 100
for x in 0.0 : 2*pi/N : 2*pi*(N-1)/N
    println(x)
end

Is there any way to avoid the ugliness of this for loop?

julia
4 Answers

Yes, there is

N = 100
for x in range(0; step=2π/N, length=N)
    println(x)
end
user_178922160

Maybe not the most elegant way... take the first n-1 elements

r = 0.0 : 2*pi/N : 2*pi
r = Iterators.take(r,length(r)-1)
user_20010170

Unfortunately, inclusive ranges (and 1-based indexing) is baked into the idioms of Julia at a fundamental level.

However, for this specific case, do note that stepping with floating point values can be problematic, as adding N values might be less than, equal to, or greater than the final value, giving different results for the for loop. Although julia tries really hard, there's no way to quite do the right thing in all circumstances. As a bonus, working in integer values only for the ranges simplifies things. You might want to consider:

for ix in 0:N-1
    x = ix * 2 * pi / N
    println(x)
end

Alternatively, the range() function has a form with a len parameter:

for x in range(0, 2*pi*(N-1)/N, length=n)
    println(x)
end

Or indeed, combining this with the other answer of only taking (N-1) could work.

Aaron_154640

You could actually define your own operator such as:

▷(a,b) = a:b-1

Now you can write:

julia> 3▷6
3:5

Julia also natively supports custom indices for arrays. There is a package CustomUnitRanges that is maybe an overkill here.

user_99577100
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