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Julia: Should arrays start with 0 or 1?

Swastik Baranwal
A noob
・2 min read

Arrays in the Julia programming language are somewhat different from arrays in other programming languages. Not because of different behavior, but because they are start at 1 instead of 0. It's because Julia is used for mathematics , machine learning and scientific etc. Where calculation as mentioned, maybe a bit of confusion when interfacing to the external (non Fortran/Matlab) world but this interfacing doesn't have to be done with arrays if this should be a problem.

If you try to access the array by using zero then it will result an error like the above code:

> [2,3,4,5][0]
ERROR: BoundsError: attempt to access 4-element Array{Int64,1} at index [0]
Stacktrace:
 [1] getindex(::Array{Int64,1}, ::Int64) at ./array.jl:729
 [2] top-level scope at none:0

But using one works fine

> [2,3,4,5][0]
   1

Arrays should start at 1 because as people count starting from one. The thing with 0-based indexing is that you always then have to write code of the type for i=0:len(a)-1 when iterating. Either ways, there is always some indexing arithmetic.

Most of people would hate Julia arrays because they do not start with 0 like other languages. Most languages are inspired from C so they have array index from 0. There's a special reason especially for C i.e. the name of an array is a pointer, which is a reference to a memory location. Therefore, an expression *(arr + n) or arr[n] locates an element n-locations away from the starting location because the index is used as an offset.

But all languages do not have start with index 0 such as MATLAB, Lua, R etc because most of the tasks that Matlab is used for, e.g. physics and engineering, use the convention of indices starting at 1 in most of the literature, so people working in these fields do not need to convert their algorithms by subtracting 1 from everything.

Hence, I believe that Julia arrays should start from one because it's made for these reasons. But I think array index with 0 are needed because of representation of memory offset as they are stored in continuous addresses especially languages like C, C++ and Java.

Discussions:
https://discourse.julialang.org/t/whats-the-big-deal-0-vs-1-based-indexing/1102
https://github.com/julialang/julia/issues/558
https://groups.google.com/forum/?hl=en#!topic/julia-dev/tNN72FnYbYQ
https://en.wikipedia.org/wiki/Comparison_of_programming_languages_(array)#Array_system_cross-reference_list
http://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html

Learn more about Julia Arrays:
https://docs.julialang.org/en/v1/base/arrays/
https://en.wikibooks.org/wiki/Introducing_Julia/Arrays_and_tuples

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