CODEWITHSUNDEEP
haskellrecursion
user6929012
user6929012

Reputation:

Haskell - unmodified variable in a recursive function

I have a list of char and integer like [('1',1),('2',2),('3',3),('4',4),('5',5)] and want to turn the integers into the percentage each number count for the total such as [('1',7),('2',13),('3',20),('4',27),('5',33)]. I have tried a recursive function which takes a parameter as (c,i):rest and then divide the i by the total and then call the function with rest. But after every single loop, the total has changed. So is there any way I declare the total from start and use it over and over like other languages.

Upvotes: 1

Views: 122

Answers (1)

epsilonhalbe
epsilonhalbe

Reputation: 15959

You need to calculate the total in advance - you can use something like 

f :: Integral b => [(a,b)] -> [(a,b)]
f lst = let total = sum $ map snd list
         in map (\(x,y) -> (x,(100 * y)`div` total)) lst

Note: it would be a good idea to collect the Integral-values associated to each character beforehand, this makes the output a bit more clear (in my opinion), but this would be an exercise for the astute reader.

To make this function more clear - I would also recommend introducing newtypes for Value and Percentage such that you never try to add values with percentages.

newtype Value a = V {extractV :: a}
newtype Percentage = P {percent :: Integer}

f :: Integral b => [(a,Value b)] -> [(a,Percentage)]

Upvotes: 2

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