loading hash-table from a file?

loading hash-table from a file?

[ishi soichi]

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I have never used hash-table of Emacs Lisp but I believe it's useful as a
database.

Say, I have a hundred key-value pairs, which are to be stored as
hash-table.
Can I save this as a (text?) file so that Emacs can load it when booting up?

I am a little confused because if I use (cons key value), it outputs "(key
. value)" which can be written in a regular file.
If I wish to find the value from a key, all I need to do is to simply
search through the file.

Do you think I can save the database using hash-table like this?

soichi

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Re: loading hash-table from a file?

[Valentin Baciu]

On Thu, Jan 5, 2012 at 7:16 AM, ishi soichi <soichi777@gmail.com> wrote:
> I have never used hash-table of Emacs Lisp but I believe it's useful as a
> database.
>
> Say, I have a hundred key-value pairs, which are to be stored as
> hash-table.
> Can I save this as a (text?) file so that Emacs can load it when booting up?
>
> I am a little confused because if I use (cons key value), it outputs "(key .
> value)" which can be written in a regular file.
> If I wish to find the value from a key, all I need to do is to simply search
> through the file.
>
> Do you think I can save the database using hash-table like this?
>
> soichi

In my Emacs 24, I can read back a printed (simple) hash table. I am
not sure weather using more complex data types as values will also
work.

;; Writing the hash table to a "database" file

(with-current-buffer (find-file-noselect "/tmp/x")
  (let ((h (make-hash-table)))
    (puthash 'a 0 h)
    (puthash 'b 1 h)
    (insert (format "%s" h))
    (save-buffer)))


;; Reading back the hash-table object

(type-of (read (find-file-noselect "/tmp/x")))
;; hash-table

Re: loading hash-table from a file?

[Eric Abrahamsen]

On Thu, Jan 05 2012, ishi soichi wrote:

> I have never used hash-table of Emacs Lisp but I believe it's useful
> as a database.
>
> Say, I have a hundred key-value pairs, which are to be stored as
> hash-table. 
> Can I save this as a (text?) file so that Emacs can load it when
> booting up?
>
> I am a little confused because if I use (cons key value), it outputs
> "(key . value)" which can be written in a regular file.
> If I wish to find the value from a key, all I need to do is to simply
> search through the file.
>
> Do you think I can save the database using hash-table like this?
>
> soichi
>
>

I found this on the internet (presumably authored by someone with the
initials T.V.), which does what you're asking (I used it to persist a
hash-table that I load on startup). I don't really know if it's superior
to the previous reply, but it certainly works. It produces a *.elc file,
which can be loaded with `load' (provided it's in your load-path, of
course). Whatever symbol name you originally dumped then becomes defined
again.

Eric

--8<---------------cut here---------------start------------->8---
(defun tv-dump-object-to-file (obj file)
  "Save symbol object `obj' to the byte compiled version of `file'.
 `obj' can be any lisp object, list, hash-table, etc...
 `file' is an elisp file with ext *.el.
 Loading the *.elc file will restitute object."
  (require 'cl) ; Be sure we use the CL version of `eval-when-compile'.
  (if (file-exists-p file)
      (error "File already exists.")
    (with-temp-file file
      (erase-buffer)
      (let* ((str-obj (symbol-name obj))
	     (fmt-obj (format "(setq %s (eval-when-compile %s))" str-obj str-obj)))
	(insert fmt-obj)))
    (byte-compile-file file) (delete-file file)
    (message "`%s' dumped to %sc" obj file)))
--8<---------------cut here---------------end--------------->8---


-- 
GNU Emacs 24.0.92.2 (i686-pc-linux-gnu, GTK+ Version 2.24.8)
 of 2012-01-04 on pellet

Re: loading hash-table from a file?

[Teemu Likonen]

* 2012-01-05T10:35:18+02:00 * Valentin Baciu wrote:

> In my Emacs 24, I can read back a printed (simple) hash table. I am
> not sure weather using more complex data types as values will also
> work.
>
> ;; Writing the hash table to a "database" file
>
> (with-current-buffer (find-file-noselect "/tmp/x")
>   (let ((h (make-hash-table)))
>     (puthash 'a 0 h)
>     (puthash 'b 1 h)
>     (insert (format "%s" h))
>     (save-buffer)))

Use the %S format character to print objects in machine-readable (i.e.,
READ) format.

Re: loading hash-table from a file?

[ishi soichi]

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Thanks everyone. I think I works well!

soichi

2012/1/5 Teemu Likonen <tlikonen@iki.fi>

> * 2012-01-05T10:35:18+02:00 * Valentin Baciu wrote:
>
> > In my Emacs 24, I can read back a printed (simple) hash table. I am
> > not sure weather using more complex data types as values will also
> > work.
> >
> > ;; Writing the hash table to a "database" file
> >
> > (with-current-buffer (find-file-noselect "/tmp/x")
> >   (let ((h (make-hash-table)))
> >     (puthash 'a 0 h)
> >     (puthash 'b 1 h)
> >     (insert (format "%s" h))
> >     (save-buffer)))
>
> Use the %S format character to print objects in machine-readable (i.e.,
> READ) format.
>

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Re: loading hash-table from a file?

[Teemu Likonen]

* 2012-01-05T14:16:41+09:00 * ishi soichi wrote:

> Say, I have a hundred key-value pairs, which are to be stored as
> hash-table. Can I save this as a (text?) file so that Emacs can load
> it when booting up?

Yes. Use the Lisp object printing functions to print to a buffer: PRINT,
PRIN1 or (FORMAT "%S" ...). Then read the printed object with READ which
turns it to a Lisp object again.

Here's an example of the idea:


    ;; Print
    (with-temp-file "/tmp/test"
      (let ((ht (make-hash-table)))
        (puthash 'a 1 ht)
        (puthash 'b 2 ht)
        (print ht (current-buffer))))


    ;; Read
    (with-current-buffer
        (find-file-noselect "/tmp/test")
      (let ((ht (read (current-buffer))))
        (list (gethash 'a ht)
              (gethash 'b ht))))

Re: loading hash-table from a file?

[Thierry Volpiatto]

Eric Abrahamsen <eric@ericabrahamsen.net> writes:

> On Thu, Jan 05 2012, ishi soichi wrote:
>
>> I have never used hash-table of Emacs Lisp but I believe it's useful
>> as a database.
>>
>> Say, I have a hundred key-value pairs, which are to be stored as
>> hash-table. 
>> Can I save this as a (text?) file so that Emacs can load it when
>> booting up?
>>
>> I am a little confused because if I use (cons key value), it outputs
>> "(key . value)" which can be written in a regular file.
>> If I wish to find the value from a key, all I need to do is to simply
>> search through the file.
>>
>> Do you think I can save the database using hash-table like this?
>>
>> soichi
>>
>>
>
> I found this on the internet (presumably authored by someone with the
> initials T.V.), which does what you're asking (I used it to persist a
> hash-table that I load on startup). I don't really know if it's superior
> to the previous reply, but it certainly works. It produces a *.elc file,
> which can be loaded with `load' (provided it's in your load-path, of
> course). Whatever symbol name you originally dumped then becomes defined
> again.
>
> Eric
>
> (defun tv-dump-object-to-file (obj file)
>   "Save symbol object `obj' to the byte compiled version of `file'.
>  `obj' can be any lisp object, list, hash-table, etc...
>  `file' is an elisp file with ext *.el.
>  Loading the *.elc file will restitute object."
>   (require 'cl) ; Be sure we use the CL version of `eval-when-compile'.
>   (if (file-exists-p file)
>       (error "File already exists.")
>     (with-temp-file file
>       (erase-buffer)
>       (let* ((str-obj (symbol-name obj))
> 	     (fmt-obj (format "(setq %s (eval-when-compile %s))" str-obj str-obj)))
> 	(insert fmt-obj)))
>     (byte-compile-file file) (delete-file file)
>     (message "`%s' dumped to %sc" obj file)))

I use this always to save emacs session (buffers and variables), but it
have limitations on complex hash-tables, windows objects etc...
T.V are my initials ;-)
 

-- 
  Thierry
Get my Gnupg key:
gpg --keyserver pgp.mit.edu --recv-keys 59F29997 

Re: loading hash-table from a file?

[Eric Abrahamsen]

On Sat, Jan 07 2012, Thierry Volpiatto wrote:

> Eric Abrahamsen <eric@ericabrahamsen.net> writes:
>

[...]

>>
>> I found this on the internet (presumably authored by someone with the
>> initials T.V.), which does what you're asking (I used it to persist a
>> hash-table that I load on startup). I don't really know if it's superior
>> to the previous reply, but it certainly works. It produces a *.elc file,
>> which can be loaded with `load' (provided it's in your load-path, of
>> course). Whatever symbol name you originally dumped then becomes defined
>> again.
>>
>> Eric
>>
>> (defun tv-dump-object-to-file (obj file)
>>   "Save symbol object `obj' to the byte compiled version of `file'.
>>  `obj' can be any lisp object, list, hash-table, etc...
>>  `file' is an elisp file with ext *.el.
>>  Loading the *.elc file will restitute object."
>>   (require 'cl) ; Be sure we use the CL version of `eval-when-compile'.
>>   (if (file-exists-p file)
>>       (error "File already exists.")
>>     (with-temp-file file
>>       (erase-buffer)
>>       (let* ((str-obj (symbol-name obj))
>> 	     (fmt-obj (format "(setq %s (eval-when-compile %s))" str-obj str-obj)))
>> 	(insert fmt-obj)))
>>     (byte-compile-file file) (delete-file file)
>>     (message "`%s' dumped to %sc" obj file)))
>
> I use this always to save emacs session (buffers and variables), but it
> have limitations on complex hash-tables, windows objects etc...
> T.V are my initials ;-)

Hats off to you sir! I use it (or rather, its dumped files) every day.

-- 
GNU Emacs 24.0.92.2 (i686-pc-linux-gnu, GTK+ Version 2.24.8)
 of 2012-01-04 on pellet