How do I populate dynamic arrays in Julia similar to Matlab

user_11666161 0
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My understanding of programming languages is limited, I have started 'coding' with matlab and wanted to transfer a simulation of mine from matlab to julia because there is no licensing fee. What I would like to know is in MATLAB I can auto populate array without ever initializing an array, while I know it is an inefficient way to it, I would like to know if there is similar way to do it on Julia.

Ex in MATLAB

for a in 1:10
    x(a)=a;
end

will give me an array x = [ 1 2 3 4 5 6 7 8 9 10], is there a similar way to do that in julia? The way I have been doing it is declaring an empty array using Float64[] and append to it but it doesn't work the same way if the array is multidimensional.

my implementation in Julia for a 1D array

x = Float64[]
for a in 1:10
    append!(x,a)
end

Any help regarding this will be greatly appreciated. Thank you!!!

julia dynamic-arrays matlab
2 Answers

MATLAB explicitly warns against the way you write this code and advises to preallocate for speed.

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Julia, OTOH, cares more about performance and prohibits such pattern from the beginning. At the same time, it allows for more convenient and fast alternatives to do the same task.

julia> x = [a for a = 1:10] # OR x = [1:10;]
10-element Vector{Int64}:
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10

and for 2D arrays,

julia> x = [i+j-1 for i = 1:5, j = 1:5] # OR x = (1:5) .+ (1:5)' .- 1
5×5 Matrix{Int64}:
 1  2  3  4  5
 2  3  4  5  6
 3  4  5  6  7
 4  5  6  7  8
 5  6  7  8  9

And you have other convenience functions, like zeros(m,n), fill(val, dims), rand(Type, dims), etc., that you can use to initialize the arrays however you want.

user_39431700

Although @AboAmmar is correct that this generally isn't a good pattern, your code works if you use push! instead of append!. push! adds an element to a vector. append appends 2 vectors.

user_51413280
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