说我有一个自定义类型的列表,称为抵押,定义如下:
data Mortgage = Mortgage {
rate: Decimal;
issuedDate: Datetime;
amount: Decimal
} deriving (Eq, Show)
在这种特殊的一次性情况下,我想基于IssuedDate以降序对列表进行排序。我该怎么做?
答案 0 :(得分:2)
在标准库的模块DA.List
中,您将找到可以sortBy
和sortOn
的功能。
具体地说,使用sortOn
:
sortMortgages: [Mortgage] -> [Mortgage] = reverse . sortOn (\m -> m.issuedDate)
完整示例:
daml 1.2
module Main where
import DA.Date
import DA.List
data Mortgage = Mortgage {
rate: Decimal;
issuedDate: Time;
amount: Decimal
} deriving (Eq, Show)
sortMortgages: [Mortgage] -> [Mortgage] = reverse . sortOn (\m -> m.issuedDate)
testSortMortgages = scenario
let
mort1 = Mortgage with rate = 0.3; issuedDate = datetime 2007 Apr 5 14 30 05 ; amount = 1.0
mort2 = Mortgage with rate = 0.2; issuedDate = datetime 2007 Apr 5 14 30 15 ; amount = 2.0
mort3 = Mortgage with rate = 0.1; issuedDate = datetime 2007 Apr 5 14 30 10 ; amount = 3.0
mortgages = [ mort1, mort2, mort3 ]
expected = [ mort2, mort3, mort1 ]
in
assert $ sortMortgages mortgages == expected