[Haskell-beginners] Given a list of lists, how to drop the last item in each (sub)list.

[Angus Comber]

I like that :)


On 2 January 2014 15:31, <smekesis at csd.auth.gr> wrote:

> Hi Angus! Take a look at the following function:
>
> discardParityByte :: [[Integer]] -> [[Integer]]
> discardParityByte = map init
>
> It returns a list constructed by applying "init" to all items in the list
> you pass in. "init" accepts a list and returns the list without its last
> item.
>
> Stavros Mekesis.
>
>
>
> Quoting Angus Comber <anguscomber at gmail.com>:
>
>  I have a list like this:
>>
>> [[1,0,0,0,1,1,1,0,0],[1,1,1,0,1,1,1,0,0],[1,0,1,0,0,1,1,0,0]
>> ,[0,1,0,0,1,1,1,0,0],[0,0,1,0,1,1,1,0,0],[1,0,0,1,1,1,1,0,1]]
>>
>> The 'inner' list is a list of 9 items.  I want to process the list so that
>> a list of lists is returned but the 9th element in each inner list is
>> dropped.
>>
>> So the function type would be [[a]] -> [[a]]
>>
>> So to get started I wrote a function like this:
>>
>> discardparitybyte :: [[Bit]] -> [[Bit]]
>>
>> But then not sure how to transform the inner list.
>>
>> I know I can access the first inner element using take 1 list.  But how do
>> I then access/manipulate this inner list?
>>
>> discardparitybyte (x:xs) = take 9 ??? (take 1 xs) : discardparitybyte ???
>>
>
>
>
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