Re: [Haskell-beginners] Unique integers in a list

Hi Ramesh, Sorry. I was trying to solve a wrong problem. Please refer to solution provided by AbdulSattar Mohammed. Regards ________________________________ From: Ramesh Kumar To: Prasanna K Rao ; "Beginners@haskell.org" Sent: Wednesday, March 28, 2012 7:53 AM Subject: Re: [Haskell-beginners] Unique integers in a list Thanks Prasanna. Is there a base case for the solution with recursion? I'm trying with this code but I'm not getting the actual desired result: isIn :: Integer -> [Integer] -> Bool isIn _ [] = False isIn n (x:xs) = if (n == x) then True else isIn n xs unique :: [Integer] -> [Integer] unique [] = [] unique (x:xs)   = if not(isIn x xs) then [x] ++ unique(xs) else unique(xs) *Main> unique [1,2,3,4,5,4] [1,2,3,5,4]         *** should have been  [1,2,3,5] Thanks & Regards.

________________________________ From: Prasanna K Rao To: Ramesh Kumar ; "Beginners@haskell.org" Sent: Wednesday, March 28, 2012 1:40 PM Subject: Re: [Haskell-beginners] Unique integers in a list

Hi,

One way is to define a 'isin' function like this::

isin x (a:[])  = if (x == a) then True else False isin x (a:as)  = if (x == a) then True else isin x as

and use it like this::

unique (x:xs)   = if not(isin x xs) then [x] ++ unique(xs) else unique(xs)

or like this::

unique(x:xs)    = [x | x <- (x:xs), not(isin x xs)] ++ unique xs

The later being the preferred one. HTH..

Regards,

________________________________ From: Ramesh Kumar To: "Beginners@haskell.org" Sent: Wednesday, March 28, 2012 3:03 AM Subject: [Haskell-beginners] Unique integers in a list

Hi,

I've just started learning Haskell a couple of weeks ago using Simon Thompson's "Haskell: Craft of Functional Programming". There is an exercise in chapter 7 of the book which goes something like this:

Define a function of the type:     unique :: [Integer] -> [Integer] which if given a list of integers, should return a list of those integers which occur only once in the input list. Example:    unique [5,2,4,2,3,1,5,2] should result in [4,3,1]

*** The questions assumes we know only of list comprehensions and recursion.

I am guessing the solution must include something like this:

unique :: [Integer] -> [Integer] unique xs = [ x | x <- xs, isSingle x ]

My problem is in defining the function 'isSingle'.

I would greatly appreciate any pointers on this.

Many thanks. Ramesh

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