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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,

by exDM69 11y ago

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.

jules 11y ago
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.
- ViralBShah 11y ago
  Not just Matlab, but many technical computing languages use 1-based indexing. Julia was never intended to have any compatibility with Matlab.
  - jjaredsimpson 11y ago
    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.
    - eggy 11y ago
      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.
- onnoonno 11y ago
  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 :-)
  - deleted 11y ago
    [deleted]
  - jules 11y ago
    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.
ViralBShah 11y ago
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.
- gct 11y ago
  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.
chrispeel 11y ago
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 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/ 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.
- masklinn 11y ago
  > 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?
- JulianMorrison 11y ago
  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.
  - 11y ago

by exDM69 11y ago

jules 11y ago

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.

ViralBShah 11y ago
Not just Matlab, but many technical computing languages use 1-based indexing. Julia was never intended to have any compatibility with Matlab.
- jjaredsimpson 11y ago
  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.
  - eggy 11y ago
    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.
onnoonno 11y ago
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 :-)
- deleted 11y ago
  [deleted]
- jules 11y ago
  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.

ViralBShah 11y ago

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.

gct 11y ago
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.

chrispeel 11y ago

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 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/ 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.

masklinn 11y ago
> 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?
JulianMorrison 11y ago
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.
- 11y ago