3!:2 just gives a representation of the noun. JMF memory-maps a file via
the OS, so you can access the file's content as if it were just normal
memory. It will stay only on disk as long as only in-place methods are used
to change it (doing something like othervar=: +: mapped var will copy it
entirely to memory anyhow). This page
https://code.jsoftware.com/wiki/Mapped_Files and this page (basically the
same as the jmf Lab): https://code.jsoftware.com/wiki/Studio/Mapped_Files
explain how to use JMF, and how it works.
I think the two mechanisms are entirely different, and both have their
pro's and con's:
reading data from file and applying 3!:2 is far simpler than JMF, and
allows working with the data faster once read, as the data is copied to
memory. JMF mapped nouns remain on disk, and incur the corresponding
transfer speed penalty.
On the other hand JMF allows using data that doesn't fit in memory, but
requires care to only apply in-place modification and care not to read more
than fits your memory.
On Fri, 3 Feb 2023, 11:04 Ak O, <akin...@gmail.com> wrote:
> I guess one of my questions directed at how the function works under the
> hood.
>
> Is it that 3!:2 is the mechanism jmf uses to treat the map?
> How do these forms differ?
>
> Ak
>
> On Thu., Feb. 2, 2023, 22:31 Raul Miller, <rauldmil...@gmail.com> wrote:
>
> > You can measure overhead with timespacex
> >
> > Maybe you had already been doing that?
> >
> > --
> > Raul
> >
> > On Thu, Feb 2, 2023 at 11:29 PM Ak O <akin...@gmail.com> wrote:
> > >
> > > Is this less overhead than the jmf form?
> > >
> > > In your example, every case where I want to operate on a file or an
> > object
> > > within the file requires translation through the 3!:2 operator.
> > >
> > > Maybe it is functionally the same as the map_jmf_ function, or am I
> > > thinking about this incorrectly?
> > > Or can you please explain the difference.
> > >
> > > Thx
> > >
> > >
> > > Ak
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > On Thu., Feb. 2, 2023, 15:43 Don Guinn, <dongu...@gmail.com> wrote:
> > >
> > > > 'testfile.txt' fwrite~3!:1 'Hello World!';(i.3 4);<2 1$'Text Here';1
> 2
> > 3 4
> > > > 456
> > > >
> > > > 3!:2 fread 'testfile.txt'
> > > >
> > > > ┌────────────┬─────────┬───────────┐
> > > >
> > > > │Hello World!│0 1 2 3│┌─────────┐│
> > > >
> > > > │ │4 5 6 7││Text Here││
> > > >
> > > > │ │8 9 10 11│├─────────┤│
> > > >
> > > > │ │ ││1 2 3 4 ││
> > > >
> > > > │ │ │└─────────┘│
> > > >
> > > > └────────────┴─────────┴───────────┘
> > > >
> > > > On Thu, Feb 2, 2023 at 2:19 PM Ak O <akin...@gmail.com> wrote:
> > > >
> > > > > In this case the data is an array of boxes.
> > > > > The datatype is 'boxe'd.
> > > > > The data is of some shape.
> > > > >
> > > > > These things have to be preserved in order to correctly restore
> them
> > > > > later. (at some cost, up-front to specify them, afterwards to
> > recall
> > > > the
> > > > > specifics, or something else) It might be easy to write as literal,
> > but
> > > > > reverting back can present some challenges.
> > > > >
> > > > > For example:
> > > > > ary=: 'abcd';4 5 6 7; 2 2 $ 8.9 7.6 .6.5 5.4
> > > > >
> > > > > datatype ary
> > > > > boxed
> > > > >
> > > > > datatype ":ary
> > > > > literal
> > > > > ***Danger***
> > > > > $ary NB. An array of structures that preserves operational
> > > > > intention.
> > > > > 3
> > > > > $":ary NB. An array whose structure is different than its
> > > > > operational intention.
> > > > > 4 22
> > > > >
> > > > > These are different and need to be accounted for.
> > > > >
> > > > > datatype (>0{ary)
> > > > > literal
> > > > >
> > > > > datatype (>1{ary)
> > > > > Integer
> > > > >
> > > > > datatype (>2{ary)
> > > > > floating
> > > > >
> > > > >
> > > > > Each unit has a shape and a type to preserve.
> > > > >
> > > > > If I want to operate on this object with the meaning intended for
> it
> > when
> > > > > it was created, many errors can be avoided when unnecessary
> > intermediate
> > > > > conversions are avoided.
> > > > >
> > > > > Jmf allows you to operate directly without having the need to
> > > > > revert from literal to your operation/operand, datatype (with the
> > > > > associated overhead and tracking).I am not saying that there is no
> > > > overhead
> > > > > with jmf, just that the cognitive load is offset or preset because
> > jmf
> > > > > treats it for the user.
> > > > >
> > > > >
> > > > > (1!2 & 1!:/, fwrite , fread) forms.
> > > > > 1. Convert to literal.
> > > > > 2. Write literal to file.
> > > > > 3. Read literal from file.
> > > > > 4. Convert literal type to operation type
> > > > > 5. Operate with type.
> > > > > End
> > > > > ___
> > > > >
> > > > > jmf form.
> > > > > 1. Create jmf file.
> > > > > 2. Map jmf file.
> > > > > 3. Operate with file.
> > > > > End
> > > > >
> > > > >
> > > > > I am interested in understanding better how the best performance is
> > > > > achieved comparing these forms.
> > > > >
> > > > > Thoughts.
> > > > >
> > > > >
> > > > > Ak
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > On Thu., Feb. 2, 2023, 07:51 bill lam, <bbill....@gmail.com>
> wrote:
> > > > >
> > > > > > Using Jmf is overkill. Also what are the advantages of jmf over
> > > > 3!:1/3!:2
> > > > > > in this case?
> > > > > >
> > > > > > On Thu, 2 Feb 2023 at 7:17 PM Ak O <akin...@gmail.com> wrote:
> > > > > >
> > > > > > > load 'jmf'
> > > > > > > NB. Loads jmf facilities.
> > > > > > >
> > > > > > > testfile =: {2,\?50#75
> > > > > > >
> > > > > > > fn =: jpath
> > 'C:\Users\skip\J904-user\temp\foo\testfile_name.jmf'
> > > > > > > NB. Links a covername to the file path.
> > > > > > > createjmf_jmf_ fn;(([:(*&8)#);testfile)
> > > > > > > NB. Create the container for your file.
> > > > > > > NB. -fn is your reference name
> > > > > > > NB. -(([:(*&8)#);testfile) allocates the size of yor fike in
> > bytes
> > > > > > >
> > > > > > > map_jmf_ 'testfile_disk';fn
> > > > > > > NB. Maps the file to a noun 'testfile_disk'
> > > > > > > ] testfile_disk_jmf_ =: testfile
> > > > > > >
> > > > > > > unmap_jmf 'testfile_disk_jmf_'
> > > > > > > NB. Release mappings
> > > > > > > Or
> > > > > > > Exit 0
> > > > > > > Close session.
> > > > > > >
> > > > > > >
> > > > > > > New session.
> > > > > > >
> > > > > > > load 'jmf'
> > > > > > > fn =: jpath
> > > > 'C:\Users\skip\J904-user\temp\foo\testfile_name.jmf'
> > > > > > > map_jmf_ 'testfile1';fn
> > > > > > > NB. Map file
> > > > > > > ] testfile1_jmf_
> > > > > > > NB. File loaded as noun 'testfile1_jmf_'
> > > > > > >
> > > > > > > Some potential benefits of the .jmf datatype:
> > > > > > > -Preserves header and shape information.
> > > > > > > -If you want to map you file as read only, use the following
> > syntax
> > > > > > > map_jmf_ 'testfile1';fn;'';1
> > > > > > > -If you would like it to be copy-on-write use the following
> > syntax
> > > > > > > map_jmf_ 'testfile1';fn;'';2
> > > > > > >
> > > > > > >
> > > > > > > Ak
> > > > > > >
> > > > > > > On Wed., Feb. 1, 2023, 21:48 'Skip Cave' via Programming, <
> > > > > > > programm...@jsoftware.com> wrote:
> > > > > > >
> > > > > > > > I have a boxed noun:
> > > > > > > >
> > > > > > > > ] testfile =: {2,\?15#50
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> ┌────┬─────┬─────┬─────┬─────┬─────┬────┬────┬────┬────┬─────┬────┬───┬────┐
> > > > > > > >
> > > > > > > > │9 21│21 47│47 37│37 13│13 33│33 20│20 4│4 49│49 6│6 25│25
> > 33│33
> > > > 9│9
> > > > > > 6│6
> > > > > > > > 43│
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> └────┴─────┴─────┴─────┴─────┴─────┴────┴────┴────┴────┴─────┴────┴───┴────┘
> > > > > > > >
> > > > > > > >
> > > > > > > > I want to store it in the following location on my machine:
> > > > > > > >
> > > > > > > >
> > > > > > > > ]fn =. < 'C:\Users\skip\J904-user\temp'
> > > > > > > >
> > > > > > > > ┌────────────────────────────┐
> > > > > > > >
> > > > > > > > │C:\Users\skip\J904-user\temp│
> > > > > > > >
> > > > > > > > └────────────────────────────┘
> > > > > > > >
> > > > > > > > Then I will close that J session.
> > > > > > > >
> > > > > > > >
> > > > > > > > Later, I will start a new J session, and I want to read that
> > saved
> > > > > file
> > > > > > > > into a noun called 'test1'
> > > > > > > >
> > > > > > > >
> > > > > > > > What is the J code for writing the noun into a file in the
> > first
> > > > > > session?
> > > > > > > >
> > > > > > > > What is the J code to read the file into a noun in the second
> > > > > session?
> > > > > > > >
> > > > > > > > Should I use 1!2 & 1!:1, or fwrite & fread, or something
> else?
> > > > > > > >
> > > > > > > >
> > > > > > > > Where in the J doc are these file operations and their
> > tradeoffs
> > > > > > > described?
> > > > > > > >
> > > > > > > >
> > > > > > > > Skip
> > > > > > > >
> > > > > > > >
> > > > > > > > Skip Cave
> > > > > > > > Cave Consulting LLC
> > > > > > > >
> > > > >
> > ----------------------------------------------------------------------
> > > > > > > > For information about J forums see
> > > > > http://www.jsoftware.com/forums.htm
> > > > > > > >
> > > > > > >
> > > >
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> > > > > >
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