From: Niklas Brunberg
Subject: Duplicate elements in list
Date: Sat, 05 Jun 2004 15:04:25 +0000
Message-ID: <c9sndm$elq$1@news.island.liu.se>

We have a list of elements, some are duplicates. We're trying to figure
out how to find the duplicate elements and increase a counter value by 1
for each instance of the element found. The list consists of lists with
two elements, the first being the incremental counter, the second being
the string sought. Example:

((1 "one") (1 "two") (1 "three") (1 "one") (1 "four") (1 "two"))

The result should be:

((2 "one") (2 "two") (1 "three") (1 "four"))


This is the function for adding 1 (incremental counter element):

(defun add-one-to-n (indata)
   (setq n (car indata))
   (setq outdata
     (cons (+ 1 n) (cdr indata))))

Any ideas on how we should go about achieving this?

Nick and Jake

• Re: Duplicate elements in list Svein Ove Aas
  • Re: Duplicate elements in list (solved) Niklas Brunberg

From: Svein Ove Aas
Subject: Re: Duplicate elements in list
Date: Sat, 05 Jun 2004 15:22:08 +0000
Message-ID: <c9sob0$rmh$1@services.kq.no>

Niklas Brunberg wrote:

> We have a list of elements, some are duplicates. We're trying to figure
> out how to find the duplicate elements and increase a counter value by 1
> for each instance of the element found. The list consists of lists with
> two elements, the first being the incremental counter, the second being
> the string sought. Example:
> 
> ((1 "one") (1 "two") (1 "three") (1 "one") (1 "four") (1 "two"))
> 
> The result should be:
> 
> ((2 "one") (2 "two") (1 "three") (1 "four"))
> 
> 
> This is the function for adding 1 (incremental counter element):
> 
> (defun add-one-to-n (indata)
>    (setq n (car indata))
>    (setq outdata
>      (cons (+ 1 n) (cdr indata))))
> 
> Any ideas on how we should go about achieving this?

I'd use a hash table, much like this:

(defun count (list)
  (let ((hash (make-hash-table)))
    (dolist (el list)
      (incf (gethash (cadr el) hash 0) (car el)))
    (let (result)
      (maphash (lambda (key val)
                 (push (list val key) result))
         hash)
      result)))

From: Niklas Brunberg
Subject: Re: Duplicate elements in list (solved)
Date: Sun, 06 Jun 2004 09:59:17 +0000
Message-ID: <c9uptj$5kj$1@news.island.liu.se>

Svein Ove Aas wrote:
> Niklas Brunberg wrote:
> 
> 
>>We have a list of elements, some are duplicates. We're trying to figure
>>out how to find the duplicate elements and increase a counter value by 1
>>for each instance of the element found. The list consists of lists with
>>two elements, the first being the incremental counter, the second being
>>the string sought. Example:
>>
>>((1 "one") (1 "two") (1 "three") (1 "one") (1 "four") (1 "two"))
>>
>>The result should be:
>>
>>((2 "one") (2 "two") (1 "three") (1 "four"))
>>
>>
>>This is the function for adding 1 (incremental counter element):
>>
>>(defun add-one-to-n (indata)
>>   (setq n (car indata))
>>   (setq outdata
>>     (cons (+ 1 n) (cdr indata))))
>>
>>Any ideas on how we should go about achieving this?
> 
> 
> I'd use a hash table, much like this:
> 
> (defun count (list)
>   (let ((hash (make-hash-table)))
>     (dolist (el list)
>       (incf (gethash (cadr el) hash 0) (car el)))
>     (let (result)
>       (maphash (lambda (key val)
>                  (push (list val key) result))
>          hash)
>       result)))
> 

Thank you Svein Ove Aas! Solved most of our problems!

/ Niklas and Jakob