JULIA : How to permute randomly a vector in julia?
l have a vector of random numbers that l want to permute randomly using randperm() function as follows but it's not working.
X=rand(100000) # a vector of 100000 random elements
Y=randperm(X) # want to permute randomly the vector x
the returned error is : ERROR: MethodError: no method matching randperm(::Array{Float64,1}) in eval(::Module, ::Any) at ./boot.jl:237
Thank you
Answer
Use shuffle()
If your only goal is to randomly permute the vector, you can use shuffle() (part of the Random module):
julia> using Random;
julia> X = collect(1:5)
5-element Array{Int64,1}:
1
2
3
4
5
julia> shuffle(X)
5-element Array{Int64,1}:
5
4
1
2
3
If you don't want to allocate a new vector, but want to shuffle in place, you can use shuffle!():
julia> shuffle!(X);
julia> X
5-element Vector{Int64}:
3
4
2
5
1
randperm()
randperm() accepts an integer n and gives a permutation of length n. You can use this ordering to then reorder your original vector:
julia> X[randperm(length(X))]
5-element Array{Int64,1}:
3
4
1
2
5
Bonus: Sampling without replacement
You can also use StatsBase.sample() to sample the same length(X) elements from your array without replacement:
julia> import StatsBase;
julia> StatsBase.sample(X, length(X), replace=false)
5-element Vector{Int64}:
5
2
4
1
3