3!:2 can construct an arbitrary nested J array and 3!:1 can serialize an arbitrary nested J array. The cost of using this mechanism is typically considerably lower than the cost of reading a file.
(There's another potential approach, involving cdcallback, but the overhead and complexity of using that mechanism would not likely lead to a better result.) I hope this helps. -- Raul On Thu, Sep 24, 2020 at 4:51 PM 'Zhihao Yuan' via Source <[email protected]> wrote: > > On Thu, Sep 24, 2020 at 12:44 PM Eric Iverson <[email protected]> > wrote: > > > > > It should be possible to package it as an addon. The addon would include > > shared libraries for the platforms of interest (windows/linux/macos) and > > simple cover functions that did the cd calls to the libraries. This is how > > Jd/lapack/etc provide extensions like this. > > > You are essentially asking me to write a > new library in C, since there is no such > library from the beginning -- which may > be fine. But here are the problems I > encountered: > > 1. How do I allocate a J array before > knowing its type and shape? Because > DLL (15!:) interface wants J side to pass > such a thing into cd. The short answer is > I can't. I must use separated calls to > negotiate the type and shape, which > leads to the next question... > > 2. How to pass FILE* to DLL from J? > All I can access from J code is file number; > DLL doesn't know what that is. This implies > that I may have to pass only filenames and > open a file twice -- first to parse its header, > then to load its data. But there is no > guarantee that the file is not renamed > between the two calls, or corresponds to > the same file. From a C library's point of > view, such an API will be poorly designed. > > I'm leaning towards adding this > functionality as 3!:12 and 3!:13, converting > a J array to bytes in NPYand retrieving a > J array from bytes. > > -- > Zhihao > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
