Swapping characters in a word inside elisp code

Swapping characters in a word inside elisp code

[uzibalqa]

I have a word and want to swap characters at position i with position j.

What would be a good way to do this ?  Would I need to change structure 
(to array, vector or some other thing) ?

Re: Swapping characters in a word inside elisp code

[uzibalqa]

Sent with Proton Mail secure email.

------- Original Message -------
On Saturday, July 29th, 2023 at 6:03 AM, uzibalqa <uzibalqa@proton.me> wrote:


> I have a word and want to swap characters at position i with position j.
> 
> What would be a good way to do this ? Would I need to change structure
> (to array, vector or some other thing) ?
 
I have done it this way, but it fails when p > q 

How can I solve this ?

(defun cswap (wstr p q)
  "Replace characters in WSTR at positions P and Q."

  (let ( (char1 (elt wstr p))
         (char2 (elt wstr q)) )

    (if (and char1 char2)
        (concat (substring wstr 0 p)
                (char-to-string char2)
                (substring wstr (+ p 1) q)
                (char-to-string char1)
                (substring wstr (+ q 1)))) ))

RE: [External] : Swapping characters in a word inside elisp code

[Drew Adams]

> I have a word and want to swap characters at position i with position j.
> 
> What would be a good way to do this ?  Would I need to change structure
> (to array, vector or some other thing) ?

(Homework?)

Depends what you mean by swap chars in a word.
And whether your word is represented by a string,
a vector, a list...  And how you want the result:
in a separate string, vector,... or in the same
one, modified.

(Again, you don't make clear what you want.)

Here's one way to swap chars in a string
destructively:

(defun cswap (string p q)
  "Swap chars in STRING at positions P and Q.
This is a destructive operation."
  (aset string p (prog1 (aref string q)
                        (aset string q (aref string p))))
  string)

(setq s1 "123456789")
(cswap s1 3 5) ; s1 = "123654789"
               ;          ^ ^

`prog1' is often used to swap things.
A more typical use is swapping values
of two variables:

(setq start (prog1 end (setq end start)))

RE: [External] : Swapping characters in a word inside elisp code

[uzibalqa]

------- Original Message -------
On Saturday, July 29th, 2023 at 8:32 AM, Drew Adams <drew.adams@oracle.com> wrote:


> > I have a word and want to swap characters at position i with position j.
> > 
> > What would be a good way to do this ? Would I need to change structure
> > (to array, vector or some other thing) ?
> 
> 
> (Homework?)
> 
> Depends what you mean by swap chars in a word.
> And whether your word is represented by a string,
> a vector, a list... And how you want the result:
> in a separate string, vector,... or in the same
> one, modified.

I have a word and want to generate permutations of it.
And I need the ability to swap two characters at positions
i and j in word.

Just a toy project that does scrabble.

 
> (Again, you don't make clear what you want.)
> 
> Here's one way to swap chars in a string
> destructively:
> 
> (defun cswap (string p q)
> "Swap chars in STRING at positions P and Q.
> This is a destructive operation."
> (aset string p (prog1 (aref string q)
> (aset string q (aref string p))))
> string)
> 
> (setq s1 "123456789")
> (cswap s1 3 5) ; s1 = "123654789"
> ; ^ ^
> 
> `prog1' is often used to swap things.
> A more typical use is swapping values
> of two variables:
> 
> (setq start (prog1 end (setq end start)))

Re: Swapping characters in a word inside elisp code

[Marcin Borkowski]

On 2023-07-28, at 21:44, uzibalqa <uzibalqa@proton.me> wrote:

> Sent with Proton Mail secure email.
>
> ------- Original Message -------
> On Saturday, July 29th, 2023 at 6:03 AM, uzibalqa <uzibalqa@proton.me> wrote:
>
>
>> I have a word and want to swap characters at position i with position j.
>>
>> What would be a good way to do this ? Would I need to change structure
>> (to array, vector or some other thing) ?
>
> I have done it this way, but it fails when p > q
>
> How can I solve this ?
>
> (defun cswap (wstr p q)
>   "Replace characters in WSTR at positions P and Q."
>
>   (let ( (char1 (elt wstr p))
>          (char2 (elt wstr q)) )
>
>     (if (and char1 char2)
>         (concat (substring wstr 0 p)
>                 (char-to-string char2)
>                 (substring wstr (+ p 1) q)
>                 (char-to-string char1)
>                 (substring wstr (+ q 1)))) ))

I'd probably use `format', not `concat'.  Alternatively, it might be
closer to idiomatic Elisp to put the word in a buffer and perform the
swap using editing operations (though this makes more sense for larger
things like words in a sentence, and probably less so for characters in
a word).

Also, if your code works only for p < q (which I believe you without
checking myself since it's about 22:45 here and my brain doesn't
function very well), why not include a check for q < p at the beginning
and call the same function recursively with p and q swapped?

Hth,

-- 
Marcin Borkowski
http://mbork.pl

RE: [External] : Swapping characters in a word inside elisp code

[uzibalqa]

------- Original Message -------
On Saturday, July 29th, 2023 at 8:45 AM, uzibalqa <uzibalqa@proton.me> wrote:


> ------- Original Message -------
> On Saturday, July 29th, 2023 at 8:32 AM, Drew Adams drew.adams@oracle.com wrote:
> 
> 
> 
> > > I have a word and want to swap characters at position i with position j.
> > > 
> > > What would be a good way to do this ? Would I need to change structure
> > > (to array, vector or some other thing) ?
> > 
> > (Homework?)
> > 
> > Depends what you mean by swap chars in a word.
> > And whether your word is represented by a string,
> > a vector, a list... And how you want the result:
> > in a separate string, vector,... or in the same
> > one, modified.
> 
> 
> I have a word and want to generate permutations of it.
> And I need the ability to swap two characters at positions
> i and j in word.
> 
> Just a toy project that does scrabble.
> 
> > (Again, you don't make clear what you want.)
> > 
> > Here's one way to swap chars in a string
> > destructively:
> > 
> > (defun cswap (string p q)
> > "Swap chars in STRING at positions P and Q.
> > This is a destructive operation."
> > (aset string p (prog1 (aref string q)
> > (aset string q (aref string p))))
> > string)

I had made a function to do it but the changes were local (temporary)
because I was using setq.
 
> > (setq s1 "123456789")
> > (cswap s1 3 5) ; s1 = "123654789"
> > ; ^ ^
> > 
> > `prog1' is often used to swap things.
> > A more typical use is swapping values
> > of two variables:
> > 
> > (setq start (prog1 end (setq end start)))