int -> [int] convert

Question

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Split a number into its digits with Haskell

how can i convert integer to integer list Exmple: input: 1234 output:[1,2,3,4] any idee about this problem ?

Solution 1

Solution:

digs 0 = []
digs x = digs (x `div` 10) ++ [x `mod` 10]

Source: link

Solution 2

This sounds like homework. Here's a general algorithm that you should be able to apply in Haskell:

1. Convert the integer to a string.
2. Iterate over the string character-by-character.
3. Convert each character back to an integer, while appending it to the end of a list.

Good luck.

Solution 3

Using integer arithmetic:

digits' 0 = []
digits' n = n `rem` 10 : digits (n `quot` 10)
digits n = reverse (digits' n)

Solution 4

What about this quite simple solution?

import Data.Char (digitToInt)

int2intList :: Integral i => i -> [Int]
int2intList s = map digitToInt $ show s

main = print $ int2intList 12351234999123123123

gives [1,2,3,5,1,2,3,4,9,9,9,1,2,3,1,2,3,1,2,3]

This one is possible and a bit more universal, too:

int2intList :: (Read i, Integral i) => i -> [i]
int2intList s = map (read.(:[])) $ show s

main = print $ int2intList 12351234999123123123

Solution 5

Alternatative solution using unfoldr:

import List
digits = reverse . unfoldr nextDigit
        where nextDigit 0 = Nothing
              nextDigit x = Just (r, q) where (q, r) = quotRem x 10

View more solutions

Comments

[marco]

I thank you very much that was the code i needed. and thanks for the other replies. cheers

[Chris Dodd]

Only problem is that digits 0 gives you any empty list, but that's trivial to fix. Also doesn't work for negative numbers, but its not clear what the right answer is in that case

[sepp2k]

@Chris: It does work for negative numbers. digits (-42) returns [-4, -2] which seems sensible to me.