
Re: Compile function and AppendTo for lists (vrs. 8.0.4)
Posted:
Jan 26, 2012 3:30 AM


Hi,
using Oleks Internal`Bag suggestion, think of a list as a bag of numbers and you can use this as replacement for the lists in your compile. Using Oleks appendto version as comparison
appendTo = Compile[{{k, _Integer, 0}}, Module[{mat = {{0, 0}}, i = 0}, For[i = 1, i <= k, i++, AppendTo[mat, {1, i}]]; Rest[mat]]]
and here is the Internal`Bag implementation
AppendTo[$ContextPath, "Internal`"]; appendBag = Compile[{{k, _Integer}}, Module[{p = Bag[], i = 1, tmpBag}, For[i = 1, i <= k, ++i, tmpBag = Bag[]; StuffBag[tmpBag, 1]; StuffBag[tmpBag, i]; StuffBag[p, tmpBag]; ]; Table[BagPart[BagPart[p, i], All], {i, k}] ] ];
Speedtest shows
In[55]:= First /@ {AbsoluteTiming[appendTo[10^5]], AbsoluteTiming[appendBag[10^5]]}
Out[55]= {14.559237, 0.149063}
that the bag implementation is about 100 times faster. Unfortunately there doesn't exist much documantation about this. One place to look is here http://stackoverflow.com/a/6795762/1078614 where Daniel gives some insights into the usage.
Hope this helps.
Cheers Patrick
On Tue, 20120124 at 05:06 0500, kris wrote: > Hi > > I have some trouble with my code and would like ask for your help. In > general it is about appending data in form of a list to an existing > list in a compiled function. As far as I understand Mathematica is not > supporting what I am asking for. In order to understand the problem in > more detail I present some "toy" code below. > > test=Compile[{{k,_Integer}}, > Module[{mat={}}, > For[i=1,i<=k,i++, > AppendTo[mat,{1,i}]; > ]; > mat > ] > ]; > > test[2] > (*which produces an error*) > > Appending data in form of numbers for example works just fine but not > with lists. Can anybody explain why Mathematica does not support > appending lists to lists for compiled function? As an alternative I > tried Reap and Sow, which also produces an error. > > However, what seems funny is the following code: > > mat={}; > test=Compile[{{k,_Integer}}, > For[i=1,i<=k,i++, > AppendTo[mat,{1,i}]; > ]; > ]; > > test[2];mat > > The above code produces the result that I was looking for in a > cumbersome way. I would like to prefer compile code which produces the > same result without calling the list mat again. > > Thanks for help I do appreciate it. > Cheers, > Kris >

