I'm beginning to wonder whether I can't just use a mixture of
hfd, dfh and a.i. to do what I need.
For example,
str =: 'notation as a tool of thought'
1 (3!:3) str
gives a literal array:
e1000000
02000000
1d000000
01000000
1d000000
6e6f7461
74696f6e
20617320
6120746f
6f6c206f
66207468
6f756768
74000000
A lot of the words here are not needed for my purposes. (By the way, I have a
subquestion: why is the top row of my literal array coloured black while the
rest of the array is purple? I have not been playing with the qtide configs, so
I assume there is some meaning here).
Anyway, I can get my hex string by doing
,/ hfd a.i. str
For floats, I will definitely need 3!:5.
Perhaps I'm confused, but it looks like hfd,dfh,a.i. (and a.{~) would suffice.
Jon
> Date: Wed, 21 Jan 2015 20:05:16 -0800
> From: [email protected]
> To: [email protected]
> Subject: Re: [Jprogramming] J Equivalent of Python Struct.Pack/Unpack
>
> Have you looked at 3!:4 and 3!:5 ?
>
>
>
> On Wed, Jan 21, 2015 at 7:56 PM, Jon Hough <[email protected]> wrote:
>
> > Basically, I am hoping to pack data in J and be able to unpack in Python,
> > or any other language (and vice versa).
> > Thats why I am a little concerned about these 5 extra words added.
> >
> > --- Original Message ---
> >
> > From: "'Pascal Jasmin' via Programming" <[email protected]>
> > Sent: January 22, 2015 12:23 PM
> > To: [email protected]
> > Subject: Re: [Jprogramming] J Equivalent of Python Struct.Pack/Unpack
> >
> > 3!:3 is the easiest way to see those extra bytes.
> >
> > I don't know if you have a very narrow constant rank and shape format, but
> > even if you did, you could read it from the file rather than assume it is
> > in expected format.
> >
> > using the reference page and simple examples as below
> > 3!:3 ] 5
> > 3!:3 ] <5
> > 3!:3 ] <5;3
> >
> > Something interesting about the format is that adding an extra level of
> > boxing around data, doesn't change any of the data offsets within the
> > data. It just adds a 5 word header to it.
> >
> > ----- Original Message -----
> > From: Jon Hough <[email protected]>
> > To: "[email protected]" <[email protected]>
> > Cc:
> > Sent: Wednesday, January 21, 2015 7:49 PM
> > Subject: Re: [Jprogramming] J Equivalent of Python Struct.Pack/Unpack
> >
> > It seems, if I want to send the data over a network, I'm going to have to
> > strip off several bytes after packing, because
> > x 3!:1
> > puts on several bytes on the front of the result. e.g. flag, type, num of
> > elements etc. Is this normal to do this?
> >
> > > Date: Wed, 21 Jan 2015 13:04:57 +0900
> > > From: [email protected]
> > > To: [email protected]
> > > Subject: Re: [Jprogramming] J Equivalent of Python Struct.Pack/Unpack
> > >
> > > Thanks.
> > > I am working on a small project in which I need to use these binary
> > string conversions and parse them in other languages, eg python.
> > >
> > > I am hoping if I use 3!: 1 then I can unpack in Python.
> > >
> > > --- Original Message ---
> > >
> > > From: "Raul Miller" <[email protected]>
> > > Sent: January 21, 2015 10:57 AM
> > > To: "Programming forum" <[email protected]>
> > > Subject: Re: [Jprogramming] J Equivalent of Python Struct.Pack/Unpack
> > >
> > > I usually use 3!:4 and 3!:5 when reading objects streamed to file from
> > > someone else's code. I wind up writing a read verb (and a write verb)
> > > for every "type" which reads its stuff starting at a global offset
> > > into the reference character array and then updates that offset to
> > > point at the end. If there's ever an array of them, the dyadic form of
> > > the verb reads x of them. (And one dimension is sufficient in this
> > > context.)
> > >
> > > I can tell my code is correct when it can read a file to my internal
> > > representation and write it back out without introducing any defects
> > > on my test data set. Except I can also identify bugs in the original
> > > code when coding to spec requires that what I write back out differs
> > > from what I read in. That can get annoying sometimes (it means that
> > > for complete correctness I need to represent the buggy data - that's
> > > the sort of thing that makes me feel like abandoning a project or at
> > > least wish I could replace larger parts of the system).
> > >
> > > It's very "forth-like" in feel, and verbose. And some types require a
> > > bit of manipulation after the initial conversion, to make things
> > > correct. But, this seems to me to be a fairly appropriate match to the
> > > problem.
> > >
> > > Your mileage may vary.
> > >
> > > Thanks,
> > >
> > > --
> > > Raul
> > >
> > > On Tue, Jan 20, 2015 at 10:47 AM, 'Pascal Jasmin' via Programming
> > > <[email protected]> wrote:
> > > > 3!:1 is more powerful than this. Converts any noun to a binary
> > (string) representation. 3!:2 unpacks.
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: Jon Hough <[email protected]>
> > > > To: "[email protected]" <[email protected]>
> > > > Cc:
> > > > Sent: Tuesday, January 20, 2015 10:42 AM
> > > > Subject: [Jprogramming] J Equivalent of Python Struct.Pack/Unpack
> > > >
> > > > Python has a useful module called struct
> > > > https://docs.python.org/2/library/struct.html
> > > > which is useful for converting strings to packed binary data.
> > > > e.g.
> > > > data = struct.pack('B', someHexString)
> > > >
> > > > Does J have an equivalent or similar function / verb?
> > > > I spent a bit of time looking, but couldn't find anything.
> > > >
> > > > Example usage would be sending data over a network.
> >
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
