How can I get the size of an array in Julia?

I'm trying to run the following piece of code:

function inversePoly(A::Array{Int64,1}, B::Array{Int64,1}) n = size(A) retVal = A[end] / B[end] i = 1 while i != n retVal = (retVal + 1 / B[n - i]) * A[n - i] i += 1 end return retVal end inversePoly(Array(3:4), Array(4:5)) 

However, Julia gives me the following error:

LoadError: MethodError: no method matching -(::Tuple{Int64}, ::Int64) Closest candidates are: -(!Matched::Complex{Bool}, ::Real) at complex.jl:298 -(!Matched::Missing, ::Number) at missing.jl:97 -(!Matched::Base.CoreLogging.LogLevel, ::Integer) at logging.jl:107 ... in expression starting at /home/francisco/Julia/abc.jl:12 inversePoly(::Array{Int64,1}, ::Array{Int64,1}) at abc.jl:6 top-level scope at none:0 

The 6th line would be

retVal = (retVal + 1 / B[n - i]) * A[n - i] 

This means that the statement

n = size(A) 

Is saving a tuple in the variable n instead of an integer

How can I get an integer representing the number of elements in A?

Thanks in advance

1 Answer

Here is how you should use size:

julia> x = [1,2,3] 3-element Array{Int64,1}: 1 2 3 julia> size(x) (3,) julia> size(x)[1] 3 julia> size(x, 1) 3 

so either extract the first element from size(x) or directly specify which dimension you want to extract by passing 1 as a second argument.

In your case, as A is a Vector (it is single dimensional) you can also use length:

julia> length(x) 3 

Which gives you an integer directly.

The difference between length and size is the following:

• length is defined for collections (not only arrays) and returns an integer which gives you the number of elements in the collection
• size returns a Tuple because in general it can be applied to multi-dimensional objects, in which case the tuple has as many elements as there are dimensions of the object (so in case of Vector, as in your question, it is 1-element tuple)