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Comment by ogogmad | Hacker News Reader

  - Arrays start at one

Why is this such a big deal? You just change the range of your for-loops from 0<=i<n to 1<=i<=n. Are you using cyclic buffers?

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It matters when doing multidimensional index arithmetic. The formulae for ranking and unranking multi-dimensional to flat indexes are neater with 0-indexing than with 1-indexing.

Julia has really nice abstractions for dealing with this. Things for which you might do such calculations in other languages can often be done in a way generic to the number of dimensions, as well as the initial index, using CartesianIndices & friends. And this should be zero cost.

Almost all languages above the C level has nice abstractions for this, but you still sometimes need to do it for various reasons. Basically, whenever the indexes don't matter, then 1-indexing and 0-indexing are equivalently good, but when they do matter, then 0-indexing leads to neater calculations.

OffsetArrays.jl is your friend.

I'm working on a project where indexing naturally runs from -n to n. I kludged the usual index hackery and was so plagued with off-by-one errors that I gave up on it. Then I remembered Tim Holy had a blog post about OffsetArrays.jl and started using that.

Problem solved.

Seriously, the most annoying thing I find about Julia is that the various packages fairly often have "creative" names, that make it difficult discover that they might actually be useful.

YMMV.

> I'm working on a project where indexing naturally runs from -n to n. I kludged the usual index hackery and was so plagued with off-by-one errors that I gave up on it. Then I remembered Tim Holy had a blog post about OffsetArrays.jl and started using that.

Ah, thank you. I've been tinkering around with Julia, and was trying out 2D random walks. Not being able to use a 2 dimensional array and store the position [0, 0] confused me. I ended up starting at X,X (where X > total number of moves) and then got stuck with plotting it nicely, because I wanted the plot axes to show how far it had moved, not X +- how far it had moved.

There are plenty of matrix uses where 1-indexing is more natural. I think the main reason Julia uses it is to be more consistent with Matlab.

Abstraction discovery is a hard problem in general. Good names help, but there's probably more we can do. Tooling finding a common pattern that the abstraction eliminates, perhaps?

I guess it could poke you every time you say `strides(A)`?

Here's a recent example of an upgrade, from code with stride calculations to a more abstracted version, which is generic to offsets & number of dimensions:

https://github.com/JuliaLang/julia/pull/37367/files#diff-29c...

Fair enough. But is this a common enough occurrence in the life of a programmer that it's worth being a religious extremist about?

No need for an inquisition. In both Fortran and Julia you can set your index origin to be whatever works best for the problem you are expressing.

It's in a list of annoyances, together with 16 others. I don't think anyone is being "a religious extremist about" it...

In Fortran, you can start the index from any number you want. A(-10:-3) is a completely valid slice or full array declaration, so are A(0:7) or A(1:8). and this feature is absolutely useful in scientific computing.

I also didn't think it was a big deal - I write a lot of lua, and I love lua - but every time I have to do anything involving modulo maths and arrays it's a pain in the ass.

Julia makes it easier for example with functions that handle mod in the context of 1-indexed arrays (if you don't want to use OffsetArrays).

https://docs.julialang.org/en/v1/base/math/#Base.mod1

Well, that seems cool, but isn't indexing from zero simpler?

I don't really remember if zero-indexing was a big deal when I was learning to program. Are there big advantages for non-programmers? I figure that's why Lua went the 1-index route.

>I don't really remember if zero-indexing was a big deal when I was learning to program

And neither is 1-indexing even though people are always complaining about it. I kinda like when indexing from the third element to the seventh element to be just 3:7, instead of 2:6. and the last element to be length(x) instead of length(x)-1. And that use case is much more frequent to me than creating circular buffers on an array. And in Julia you can just use begin:end as well, or any iterator, it's really overall a non-issue for me.

Not sure about Lua, but in Julia (and Matlab, and R) is just because they actually have vectors/matrices types that have a convention that predates even programming, while it makes sense for languages that an array is basically a memory offset (that maps to a pointer arithmetic logic) to start in 0.

Array should start from any index scientist wishes. That is how it is done in Fortran.

Dijkstra on the matter: https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/E...

Dijkstra has a certain tone. He can make his opinions sound almost like a mathematical proof. But when you dig into it, he just says 0-based is "nicer".

The points he makes are so extremely minor... You could just as easily say that natural language and mathematical convention are index-1.

I never understood the fascination with preferring "the element at zero offset from the start" to "the first element" - and I don't think djiskarta makes a compelling argument.

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