And more important question - is it possible to generalize the copying of python array object to managed C# array object without knowing the data type/size/length?
On Wed, Nov 5, 2014 at 8:58 AM, Denis Akhiyarov <denis.akhiya...@gmail.com> wrote: > How to copy unmanaged array (python list/tuple or numpy array) into > managed C# array? I guess using Marshal.Copy, but can anyone point to > example? > > Thanks, > Denis > > On Thu, Oct 30, 2014 at 12:19 PM, Nikhil Garg <nikhilgarg....@gmail.com> > wrote: > >> Thanks Brad and Jeff for the detailed info. For now, fromiter is serving >> me well and has reduced my processing time considerably, so I am just going >> to stick with it. >> >> >> On 29 October 2014 11:04, Jeffrey Bush <j...@coderforlife.com> wrote: >> >>> I finally have a chance to chime in, and Bradley is exactly right. >>> Marshall.Copy copies the raw data, and apparently your file library does >>> not store that data in a nice, contiguous, manner. While it is highly >>> likely that copying all the data to an array in C# will be faster than the >>> fromiter in Python, I am unsure if copying all the data to an array in C# >>> then copying all the data again to a numpy array will be faster than >>> fromiter (cause you have to copy it twice). The exception is if the file >>> library has a function like ToArray that is optimized to copy the data to a >>> linear chunk of data. So, what type is "Data"? >>> >>> Another factor is how long the chunk of data you are copying is. You say >>> the last axis is only 400 elements long. Check out my code and you will see >>> that at 400 elements long, fromiter is actually the fastest (at least when >>> I tried). An example run: >>> >>> Copy using for loop in 0.000884 sec >>> Copy using fromiter in 0.000144 sec # fastest >>> Copy using fromstring in 0.001460 sec # fairly slow, 10.3x slower than >>> fromiter >>> Copy using Marshal.Copy in 0.001680 sec # slowest, 11.7x slower than >>> fromiter >>> >>> I start to do better with Marshal.Copy then fromiter around 5000 >>> elements copied. This is because the overhead of the mass copies is high >>> but adding each element doesn't take much time. fromstring has a lower >>> overhead but slightly longer per-element time (fromstring is better than >>> Marshal.Copy until ~200,000 elements). >>> >>> So you might be doing as good as you can possibly do. If I knew more >>> about your file format library I might be able to provide more insight. >>> >>> Jeff >>> >>> On Tue, Oct 28, 2014 at 2:45 PM, Bradley Friedman <b...@fie.us> wrote: >>> >>>> Well it makes sense to me that doing it via an iterator, and element at >>>> a time, would be slow. There’s a lot of call overhead associated with each >>>> iteration step. Whether it’s done in .net, or in python, or a call from >>>> one to the other, it will be slow. It’s still a call where you’d be better >>>> off copying whole buffers. >>>> >>>> Ideally you’d pull the data into as simple and raw a data structure as >>>> you can on the dotnet side, in a buffered manner. Then you’d execute a >>>> movement of the data across, a reasonably sized chunk of buffer at a time. >>>> This will reduce call overhead and also allow read-ahead caching to do its >>>> thing on the file-access side of things. >>>> >>>> Your suggestion of loading into a .net array and then moving that array >>>> over, makes sense. But I think it comes down to what you can do with the >>>> third party file-format library. If its not going to provide you with the >>>> data as some kind of buffer with a cohesive and known format in memory, >>>> you’re not really going to be able to move it over without iterating over >>>> it and reformatting it at some point. >>>> >>>> Specifically, I’d point to Jeffery’s original caveat: >>>> >>>> "but does involve a number of assumptions (for example that the data in >>>> the two arrays are laid out in the same way)." >>>> >>>> The question is: is there a way to get the data off of disk and in >>>> memory from dotnet library, where its layout in memory is known, and >>>> something you want exactly as it is, but in python? If so, you should be >>>> able to use the methods from the afore linked thread. If not, you’re >>>> probably stuck iterating somewhere to reformat it, no matter what. Which >>>> is probably why you got garbage back. I’m guessing the object returned >>>> from the dotnet file-format-library isn’t laid out right, as suggested in >>>> the afore referenced caveat. >>>> >>>> >>>> > On Oct 28, 2014, at 9:55 AM, Nikhil <nikhilgarg....@gmail.com> wrote: >>>> > >>>> > Hello, >>>> > Yeah, I read data from a file say at each node and each time step, >>>> but when i try to use Marshal approach i get gibberish but when i use >>>> simple iter i get correct values. i have been trying the approach used in >>>> example in the previous post and that example makes sense but it doesnt >>>> make sense when i use it in my case. I am right now assigning it to a >>>> variable, i am now thinking of exploring the possibility of saving data to >>>> a dot net array maybe using System.Array and saving data to it but not sure >>>> if that even make sense. >>>> > >>>> > Sent from my iPhone >>>> >>>> _________________________________________________ >>>> Python.NET mailing list - PythonDotNet@python.org >>>> https://mail.python.org/mailman/listinfo/pythondotnet >>>> >>> >>> >>> _________________________________________________ >>> Python.NET mailing list - PythonDotNet@python.org >>> https://mail.python.org/mailman/listinfo/pythondotnet >>> >> >> >> >> -- >> Regards >> >> Nikhil >> >> ------------------------------------------------------------------- >> Big whirls have little whirls, >> Which feed on their velocity, >> And little whirls have lesser whirls, >> And so on to viscosity >> (Richardson, 1922) >> >> _________________________________________________ >> Python.NET mailing list - PythonDotNet@python.org >> https://mail.python.org/mailman/listinfo/pythondotnet >> > >
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