[Haskell-cafe] Tuple

[Henk-Jan van Tuyl]

On Sun, 10 Apr 2011 18:49:59 +0200, Anwar Bari <noor2004 at yahoo.com> wrote:

> HI Cafe
>      I have to make a function to check that I have one occurrence of  
> the last
> element (z) of the same list [a,b] in the tuple
>
>  [([a,b],z)]
> For example
> [([1,2],3),([1,1],5),([1,3],6).......]  this is true because there is  
> one single
> z for each single list.
>
> while this one is false
> [([1,2],3),([1,2],5),([1,3],6).......] because 3&5 were found for the  
> same list
> [1,2]
>


   import Data.Function (on)
   import Data.List     (groupBy, nub, sort)

   a = [([1,2],3),([1,1],5),([1,3],6)]
   b = [([1,2],3),([1,2],5),([1,3],6)]

   check = all ((< 2) . length . nub) . groupBy ((==) `on` fst) . sort

   main = print $ check a && not (check b)

I don't know if I interpreted your specifications correctly;
this program ignores identical tuples, so
   check [([1,2],3), ([1,2],3), ([1,3],6)]
returns True; if this is not what you meant, remove the " . nub" from the  
program.

Regards,
Henk-Jan van Tuyl


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