Julia is usually very fast in nested loops, so if the they are working correctly for you, you should proabably check the performance maybe just stick with it.
Other option would be using repmat (this one is a little faster than using repeat):
[repmat(x,1,length(y))'[:] repmat(y,length(x),1)[:]]
Did some quick testing of both methods:
x=rand(1000)
y=rand(1000)
function withrepeat(x,y)
[repeat(x, inner=[size(y,1)]) repeat(y, outer=[size(x,1)])]
end
function withrepmat(x,y)
[repmat(x,1,length(y))'[:] repmat(y,length(x),1)[:]]
end
withrepeat(x,y)
elapsed time: 0.21556302 seconds (95986112 bytes allocated)
with repmat(x,y)
elapsed time: 0.075604488 seconds (56000560 bytes allocated)
Not sure why so much difference and I think there is room for improvement still.
Haven't tried the product function inside the Iterators.jl package.
Also a little bit more information here: https://groups.google.com/forum/#!topic/julia-users/dtl--SyFgwY
Hope this helps.
Tried a couple of nested loops and indeed is faster:
function withloops (x,y)
leny=length(y)
lenx=length(x)
m=leny*lenx
OUT = zeros(Float64, m,2)
c=1
for i = 1:lenx
for j = 1:leny
OUT[c,1] = x[i]
OUT[c,2] = y[j]
c+=1
end
end
return OUT
end
And, for the same rand(1000)
for x
and y
.
withloops(x,y)
elapsed time: 0.011350679 seconds (16000128 bytes allocated)