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Today's Topics:
1. Re: Beginners Digest, Vol 27, Issue 57 (Martin Tomko)
2. removing duplicate tuples (including symmetrical ones)
(Martin Tomko)
3. Re: removing duplicate tuples (including symmetrical ones)
(edgar klerks)
4. Re: removing duplicate tuples (including symmetrical ones)
(edgar klerks)
5. Re: removing duplicate tuples (including symmetrical ones)
(Martin Tomko)
----------------------------------------------------------------------
Message: 1
Date: Tue, 28 Sep 2010 10:07:13 +0200
From: Martin Tomko <[email protected]>
Subject: [Haskell-beginners] Re: Beginners Digest, Vol 27, Issue 57
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Ahaaa, the heureka moment. Stupid me, I should have tried :t null
Thanks Brent!
On 9/27/2010 6:00 PM, [email protected] wrote:
> Send Beginners mailing list submissions to
> [email protected]
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://www.haskell.org/mailman/listinfo/beginners
> or, via email, send a message with subject or body 'help' to
> [email protected]
>
> You can reach the person managing the list at
> [email protected]
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Beginners digest..."
>
>
> Today's Topics:
>
> 1. Re: matching the output of a standard function to my
> function definition (non-exhaustive pattern problem) (Brent Yorgey)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 27 Sep 2010 12:21:08 -0400
> From: Brent Yorgey<[email protected]>
> Subject: Re: [Haskell-beginners] matching the output of a standard
> function to my function definition (non-exhaustive pattern
> problem)
> To: [email protected]
> Message-ID:<[email protected]>
> Content-Type: text/plain; charset=us-ascii
>
> On Mon, Sep 27, 2010 at 06:15:22PM +0200, Martin Tomko wrote:
>
>> Dear Daniel
>> that worked perfectly, thanks for the suggestion!
>>
>> One more question: how do you use null to check for empty lists?
>> something like [] == null did not work ... just chekcing, I got my
>> orignal code to work, thanks again!
>> Martin
>>
> When in doubt, consult the types!
>
> null :: [a] -> Bool
>
> That is, null is a function for testing lists to see whether they are
> empty. So rather than 'list == null' you write 'null list'.
>
> -Brent
>
>
> ------------------------------
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
> End of Beginners Digest, Vol 27, Issue 57
> *****************************************
>
>
--
Martin Tomko
Postdoctoral Research Assistant
Geographic Information Systems Division
Department of Geography
University of Zurich - Irchel
Winterthurerstr. 190
CH-8057 Zurich, Switzerland
email: [email protected]
site: http://www.geo.uzh.ch/~mtomko
mob: +41-788 629 558
tel: +41-44-6355256
fax: +41-44-6356848
------------------------------
Message: 2
Date: Tue, 28 Sep 2010 11:33:54 +0200
From: Martin Tomko <[email protected]>
Subject: [Haskell-beginners] removing duplicate tuples (including
symmetrical ones)
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi all,
I apologize for spamming this forum so frequently, but there is noone I
can turn to around here...
I have a list of (a,a) tuples, and am trying something like nub, but
also matching for symmetrical tuples. I implemented it using the
template from delete from Prelude. Seems like my typse signature has
some troubles (Paarse error in pattern) but I am not sure where the
problem is.
removeDuplTuples :: [(a,a)] -> [(a,a)]
removeDuplTuples [] = []
removeDuplTuples [b] = [b]
-- using the syntactic sugar for single element in list
removeDuplTuples x:xs = nub (if elem (snd x,fst x) xs then
removeDuplTuples xs else [x] ++ removeDuplTuples xs)
I assume the problem lies in elem (snd x,fst x) xs but I am not sure how
to rewrite it.
Thanks for all help,
Martin
------------------------------
Message: 3
Date: Tue, 28 Sep 2010 11:44:41 +0200
From: edgar klerks <[email protected]>
Subject: Re: [Haskell-beginners] removing duplicate tuples (including
symmetrical ones)
To: [email protected]
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hi Martin,
You have some typos:
import Data.List
removeDuplTuples :: (Eq a) => [(a,a)] -> [(a,a)]
removeDuplTuples [] = []
removeDuplTuples [b] =
[b]
-- using the syntactic sugar for single element in list
removeDuplTuples (x:xs) = nub (if elem (snd x,fst x) xs then
removeDuplTuples xs else [x] ++ removeDuplTuples xs)
--------
You forgot the parenthesis. Parse error in pattern usually means a type in
the input of one of your functions. Nub needs elements that can be equal.
Nub is quitte inefficient, if your elements can be ordered, there is a more
efficient version. It is something like:
fmap head.group.sort $ [1,1,1,1,4,4,5,6,6,7,8,9]
[1,4,5,6,7,8,9]
But I haven't test it thoroughly.
Greets,
Edgar
On Tue, Sep 28, 2010 at 11:33 AM, Martin Tomko <[email protected]>wrote:
> Hi all,
> I apologize for spamming this forum so frequently, but there is noone I can
> turn to around here...
> I have a list of (a,a) tuples, and am trying something like nub, but also
> matching for symmetrical tuples. I implemented it using the template from
> delete from Prelude. Seems like my typse signature has some troubles (Paarse
> error in pattern) but I am not sure where the problem is.
>
> removeDuplTuples :: [(a,a)] -> [(a,a)]
> removeDuplTuples [] = []
> removeDuplTuples [b] = [b]
>
> -- using the syntactic sugar for single element in list
> removeDuplTuples x:xs = nub (if elem (snd x,fst x) xs then removeDuplTuples
> xs else [x] ++ removeDuplTuples xs)
>
> I assume the problem lies in elem (snd x,fst x) xs but I am not sure how to
> rewrite it.
>
> Thanks for all help,
> Martin
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
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Message: 4
Date: Tue, 28 Sep 2010 11:45:24 +0200
From: edgar klerks <[email protected]>
Subject: Re: [Haskell-beginners] removing duplicate tuples (including
symmetrical ones)
To: [email protected]
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
>You forgot the parenthesis. Parse error in pattern usually means a type in
the input of one of your functions. Nub needs >elements that can be equal.
type has to be typo.
On Tue, Sep 28, 2010 at 11:44 AM, edgar klerks <[email protected]>wrote:
> Hi Martin,
>
> You have some typos:
>
> import Data.List
> removeDuplTuples :: (Eq a) => [(a,a)] -> [(a,a)]
>
> removeDuplTuples [] = []
> removeDuplTuples [b] =
> [b]
> -- using the syntactic sugar for single element in list
> removeDuplTuples (x:xs) = nub (if elem (snd x,fst x) xs then
> removeDuplTuples xs else [x] ++ removeDuplTuples xs)
> --------
> You forgot the parenthesis. Parse error in pattern usually means a type in
> the input of one of your functions. Nub needs elements that can be equal.
>
> Nub is quitte inefficient, if your elements can be ordered, there is a more
> efficient version. It is something like:
>
> fmap head.group.sort $ [1,1,1,1,4,4,5,6,6,7,8,9]
> [1,4,5,6,7,8,9]
>
> But I haven't test it thoroughly.
>
> Greets,
>
> Edgar
>
> On Tue, Sep 28, 2010 at 11:33 AM, Martin Tomko <[email protected]>wrote:
>
>> Hi all,
>> I apologize for spamming this forum so frequently, but there is noone I
>> can turn to around here...
>> I have a list of (a,a) tuples, and am trying something like nub, but also
>> matching for symmetrical tuples. I implemented it using the template from
>> delete from Prelude. Seems like my typse signature has some troubles (Paarse
>> error in pattern) but I am not sure where the problem is.
>>
>> removeDuplTuples :: [(a,a)] -> [(a,a)]
>> removeDuplTuples [] = []
>> removeDuplTuples [b] = [b]
>>
>> -- using the syntactic sugar for single element in list
>> removeDuplTuples x:xs = nub (if elem (snd x,fst x) xs then
>> removeDuplTuples xs else [x] ++ removeDuplTuples xs)
>>
>> I assume the problem lies in elem (snd x,fst x) xs but I am not sure how
>> to rewrite it.
>>
>> Thanks for all help,
>> Martin
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>
>
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------------------------------
Message: 5
Date: Tue, 28 Sep 2010 11:57:28 +0200
From: Martin Tomko <[email protected]>
Subject: Re: [Haskell-beginners] removing duplicate tuples (including
symmetrical ones)
To: edgar klerks <[email protected]>
Cc: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hi Edgar,
thanks for the help. I wanted to first test with nub, but I still cannot
get it to work. I cannot see any missing parenthesis, but I retyped it
this way to check:
removeDuplTuples :: (Eq a) =>[(a,a)] -> [(a,a)]
removeDuplTuples [] = []
removeDuplTuples [b] = [b]
removeDuplTuples x:xs = nub(if ((snd x,fst x) `elem` xs) then
(removeDuplTuples xs) else ([x] ++ removeDuplTuples xs))
still the same error
What am I missing?
Martin
On 9/28/2010 11:45 AM, edgar klerks wrote:
> >You forgot the parenthesis. Parse error in pattern usually means a
> type in the input of one of your functions. Nub needs >elements that
> can be equal.
>
> type has to be typo.
> On Tue, Sep 28, 2010 at 11:44 AM, edgar klerks <[email protected]
> <mailto:[email protected]>> wrote:
>
> Hi Martin,
>
> You have some typos:
>
> import Data.List
> removeDuplTuples :: (Eq a) => [(a,a)] -> [(a,a)]
>
> removeDuplTuples [] = []
> removeDuplTuples [b] =
> [b]
>
> -- using the syntactic sugar for single element in list
> removeDuplTuples (x:xs) = nub (if elem (snd x,fst x) xs then
> removeDuplTuples xs else [x] ++ removeDuplTuples xs)
> --------
> You forgot the parenthesis. Parse error in pattern usually means a
> type in the input of one of your functions. Nub needs elements
> that can be equal.
>
> Nub is quitte inefficient, if your elements can be ordered, there
> is a more efficient version. It is something like:
>
> fmap head.group.sort $ [1,1,1,1,4,4,5,6,6,7,8,9]
> [1,4,5,6,7,8,9]
>
> But I haven't test it thoroughly.
>
> Greets,
>
> Edgar
>
> On Tue, Sep 28, 2010 at 11:33 AM, Martin Tomko
> <[email protected] <mailto:[email protected]>> wrote:
>
> Hi all,
> I apologize for spamming this forum so frequently, but there
> is noone I can turn to around here...
> I have a list of (a,a) tuples, and am trying something like
> nub, but also matching for symmetrical tuples. I implemented
> it using the template from delete from Prelude. Seems like my
> typse signature has some troubles (Paarse error in pattern)
> but I am not sure where the problem is.
>
> removeDuplTuples :: [(a,a)] -> [(a,a)]
> removeDuplTuples [] = []
> removeDuplTuples [b] = [b]
>
> -- using the syntactic sugar
> for single element in list
> removeDuplTuples x:xs = nub (if elem (snd x,fst x) xs then
> removeDuplTuples xs else [x] ++ removeDuplTuples xs)
>
> I assume the problem lies in elem (snd x,fst x) xs but I am
> not sure how to rewrite it.
>
> Thanks for all help,
> Martin
> _______________________________________________
> Beginners mailing list
> [email protected] <mailto:[email protected]>
> http://www.haskell.org/mailman/listinfo/beginners
>
>
>
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