算法 - 如何删除Haskell列表中的重复元素
问题描述：
我在创建一个类似于nub函数的函数时遇到了问题。
I'm having a problem creating an function similar to the nub function.
我需要这个函数来从列表中移除重复的元素。
当两个元素具有相同的电子邮件时，元素被复制，并且它应该保持较新的元素（接近列表的末尾）。
I need this func to remove duplicated elements form a list. An element is duplicated when 2 elements have the same email, and it should keep the newer one (is closer to the end of the list).
type Regist = [name,email,,...,date]
type ListRe = [Regist]
rmDup ListRe -> ListRe
rmDup [] = []
rmDup [a] = [a]
rmDup (h:t) | isDup h (head t) = rmDup t
| otherwise = h : rmDup t
isDup :: Regist -> Regist -> Bool
isDup (a:b:c:xs) (d:e:f:ts) = b==e
问题是函数不会删除重复的元素，除非它们在列表中一起出现。
The problem is that the function doesn't delete duplicated elements unless they are together in the list.
答
Slightly doctored version of your original code to make it run:
type Regist = [String]
type ListRe = [Regist]
rmDup :: ListRe -> ListRe
rmDup [] = []
rmDup (x:xs) = x : rmDup (filter (\y -> not(x == y)) xs)
结果：
Result:
*Main> rmDup [["a", "b"], ["a", "d"], ["a", "b"]]
[["a","b"],["a","d"]]