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Comment by exDM69 | Hacker News Reader

Has your stance on one-based array indexing changed in those 6 years? How many off-by-one issues have you encountered?

I'm not from a Matlab/Octave background, so one-based indexing feels really foreign to me.

For those who don't like one-based indexing, your problem is solved: there is now a package which provides two-based indexing https://github.com/simonster/TwoBasedIndexing.jl ;-)

Edit: For a history of 0-based indexing see http://exple.tive.org/blarg/2013/10/22/citation-needed/ My understanding is that with modern compilers, there's no need for 0-based indexing; you can use 0-base, 1-base, or 69-base indexing as you prefer. 0-base is applicable to people creating chips or writing hardware drivers. Most scientific programmers are not so closely tied to hardware; 1-based indexing is one of the things that helps make Julia more accessible to high-school programmers or PhD students who don't want to learn binary arithmetic.

> My understanding is that with modern compilers, there's no need for 0-based indexing; you can use 0-base, 1-base, or 69-base indexing as you prefer.

It's never been needed, Pascal had arbitrary array bounds (including negative) 50 years ago.

> 1-based indexing is one of the things that helps make Julia more accessible to high-school programmers or PhD students who don't want to learn binary arithmetic.

What does binary arithmetic have to do with anything? And have there been any study pertaining to the accessibility of 0-indexed versus 1-indexed arrays to high-scool programmers which would warrant such an assertion?

Zero based indexing counts offsets. Literally in C, you are saying "add n times sizeof(T) to the base pointer and dereference it". It rather implies arrays are contiguous in storage and lack any "holes". It's a crude but close-to-the-metal approach. C arrays are not general, they are one specific structure. An array could be implemented as a tree, but C doesn't have built-in support for that.

One based indexing counts, or labels boxes. Counting implies no "holes", but abandons any implication about how they are laid out in storage. Labelling allows treating numerical arrays as sparse hash tables, with as many "holes" as needed. It's a high level view, suited to mathy ways of thinking about data.

You can "label" by just agreeing that zero is in the set of counting numbers and labelling with those. Just because it's zero based doesn't mean it has to be an offset.

One-based is just wrong. I've never been in a zero-based language and wanted one-based, but I go the other way all the time. Arrays beginning with zero are isomorphic to the ring formed by Z modulo N, and you can use a bit mask for modulo with a power-of-two array size. It's not an "implementation detail" that arrays start with zero it's a "zero is important to mathematics" thing.

If I want to build a hash table, a power of two size for the underlying array is a nice performance optimization since you can use a bitmask instead of a modulo operation, and it makes a big performance difference, what does one-based give you other than some nebulous "it just _seems_ simpler to think about" kind of nonsense? I love how we expect people to grok the type system but we're afraid zero-based arrays will scare mathematicians off.

See: https://en.wikipedia.org/wiki/Modular_arithmetic#Integers_mo...

I feel that 1-based indexing has been the right choice, and I am aware that many do not like it. I really haven't run into off-by-one issues much, but this is probably more about how one is used to writing code. I like that you can iterate over a vector of size n, by just going from 1 to n.

Coming from a regular programming background, as opposed to a technical computing background, can certainly make this look alien. However, I think it starts feeling natural quickly. There are many other things in Julia that can take a lot longer to get used to.

It sucks for slicing though. In python (zero based), you can use 0:n to slice the entire array with a half-open interval. With one based, you have to either have a closed interval, so 1:n is the whole array (which sucks because what does an empty interval starting at 1 look like? 1:0?) Or you can have a half-open interval and index 1:n+1. I don't see what you saved yourself other than making things uglier.

For what it's worth, I've ran into this a couple of times. Maybe it's just because I'm more familiar with 0-based indexing, but I think it's not just that. In every case the 0-based indexing had fewer (+1)'s and (-1)'s than the 1-based code. For instance k%n returns a number in the range [0,n), or in Julia notation [0:n-1]. When you want to do array indexing with that, you need (k%n)+1 in Julia.

Btw, Matlab also uses 1-based indexing, no? I thought that Julia chose 1-based indexing to get brain backwards compatibility with Matlab.

Not just Matlab, but many technical computing languages use 1-based indexing. Julia was never intended to have any compatibility with Matlab.

It's just bikeshedding IMO. When I write C# code, array indices are like memory operation in my mind. When I go to Octave indices are like subscripts on sequences to me. Anyone who think it really makes a difference is being ridiculous.

I think zero based is "prettier" because of half open intervals, but it really doesn't matter.

I don't think it is bikeshedding IMO from a pure mathematics point of view. In set theory you begin with the empty set as zero, and the next integer is N+1. I find it interesting that the Julia devs have gone with APLs style of slicing, and did not move to 0-based indexing. Ken Iverson, who created APL and later the J programming language, chose 0-based indexing for J. APL has a system variable QUAD-IO that allows you to choose your indexing value of 0 or 1, which leads to many issues. Iverson's books on math (Arithmetic, Calculus, and the Concrete Math Companion (Knuth's book done in J)) all to demonstrate mathematics in J, all begin at Chapter 0. I think the choice of index in APL is a bad idea. I have run other people's code, and realized it doesn't work because they set their indexing to 1 vs. 0 for me. People and programmers can work around most things, but I think if you are a functional programmer, and mathematics is your thing, you are more comfortable with 0-based indexing. This of course does not address scientists, for whom pure mathematics is not at the forefront of whatever they are working on. I do think it leads to problems down the road for 1-based indexing.

Julia looks very interesting but honestly, exactly the 1-based indexing makes it feel really awkward and turns me off every time I think about using it somewhere.

Wouldn't it be possible to create array classes in Julia that all indexed zero-based? I would welcome a 'Julia0' fork :-)

While I agree that it's an annoyance, it's a very small annoyance. Since Julia has for loops and Julia ranges use the same 1-based convention you don't run into it often.

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