5 ms·

- 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?

adolgert 6y ago
Dijkstra on the matter: https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/E...
- ogogmad 6y ago
  The points he makes are so extremely minor... You could just as easily say that natural language and mathematical convention are index-1.
  - e12e 6y ago
    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.
- goto11 6y ago
  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".
Athas 6y ago
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.
- ogogmad 6y ago
  Fair enough. But is this a common enough occurrence in the life of a programmer that it's worth being a religious extremist about?
  - leephillips 6y ago
    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.
  - remram 6y ago
    It's in a list of annoyances, together with 16 others. I don't think anyone is being "a religious extremist about" it...
- improbable22 6y ago
  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.
  - Athas 6y ago
    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.
    - 7thaccount 6y ago
      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.
    - fghorow 6y ago
      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.
      - porker 6y ago
        > 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.
- TheRealKing 6y ago
  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.
TheRealKing 6y ago
Array should start from any index scientist wishes. That is how it is done in Fortran.
pasabagi 6y ago
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.
- ddragon 6y ago
  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 https://docs.julialang.org/en/v1/base/math/#Base.mod1
  - pasabagi 6y ago
    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.
    - ddragon 6y ago
      >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.

adolgert 6y ago

Dijkstra on the matter: https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/E...

ogogmad 6y ago
The points he makes are so extremely minor... You could just as easily say that natural language and mathematical convention are index-1.
- e12e 6y ago
  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.
goto11 6y ago
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".

Athas 6y ago

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.

ogogmad 6y ago
Fair enough. But is this a common enough occurrence in the life of a programmer that it's worth being a religious extremist about?
- leephillips 6y ago
  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.
- remram 6y ago
  It's in a list of annoyances, together with 16 others. I don't think anyone is being "a religious extremist about" it...
improbable22 6y ago
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.
- Athas 6y ago
  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.
  - 7thaccount 6y ago
    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.
  - fghorow 6y ago
    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.
    - porker 6y ago
      > 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.
TheRealKing 6y ago
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.

TheRealKing 6y ago

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

pasabagi 6y ago

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.

ddragon 6y ago
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 https://docs.julialang.org/en/v1/base/math/#Base.mod1
- pasabagi 6y ago
  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.
  - ddragon 6y ago
    >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.