Unfortunately, my happiness was a bit premature. With a simple function
like f(x)=x or f(x)=sin(x), it works, that's inlined, as it seems. If the
function is more complicated, it isn't, and we're back at many seconds, and
memory allocation of gigabytes for sorting an array of 1000000 elements. :-(
In C++11, that works:
vector<int> arr(S);
for(int i = 0, k = 0; k <= M; k++)
for(int l = k; l <= M; l++, i++)
arr[i] = (k << 16) + l;
sort (arr.begin(), arr.end(), [](int i, int j)
{
return (sf(i) < sf(j));
});
Here, sf is a more complex function, sf(i)=f[i>>16+1]+f[i&65535+1], where
the array f is precomputed
The syntax of a lambda expression (since C++11) is rather strange, but the
implementation seems to be efficient, it's actually much faster than
defining the lt function outside.
As it seems, I won't be able port that to Julia.
Am Freitag, 4. Juli 2014 15:22:08 UTC+2 schrieb Stefan Karpinski:
>
> Yes, exactly. Sorry I was not especially helpful yesterday – was on my
> phone. But you seem to have figured it out. Sorry also that this is not the
> most elegant interface. Obviously the longer term is to make passing
> functions as arguments more efficient.
>
>
> On Fri, Jul 4, 2014 at 5:36 AM, gentlebeldin <[email protected]
> <javascript:>> wrote:
>
>> I guess you mean something like this:
>>
>> julia> using Base.Order
>>
>> julia> import Base.lt
>>
>> julia> type MyNewOrdering<:Ordering
>> end
>>
>> julia> f(x::Float64)=x
>> f (generic function with 1 method)
>>
>>
>> julia> lt(o::MyNewOrdering,x::Float64,y::Float64)=f(x)<f(y)
>> lt (generic function with 9 methods)
>>
>>
>> julia> a=rand(1000000)
>> 1000000-element Array{Float64,1}:
>> ...
>>
>> julia> @time sort(a,order=MyNewOrdering())
>> elapsed time: 0.119845282 seconds (8000496 bytes allocated)
>> 1000000-element Array{Float64,1}:
>> ...
>>
>>
>> Yes, that's better, both time and memory allocation. Thank you very much!
>> :-)
>>
>> Am Donnerstag, 3. Juli 2014 21:14:05 UTC+2 schrieb Stefan Karpinski:
>>
>>> You can also define your own subtype of Order. See base/order.jl.
>>>
>>>
>
