I have a 2 lists of strings
eg:
listx = ["name","age","rank"]
input = ["name","age"]
How can I compare the two lists to check whether the listx contains "name" & "age" given in input?
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4 Answers
B is a subset of A iff B \ A is empty
so another way to do it is
import Data.List ((\\))
null (input \\ listx)
Comments
all (flip elem listx) input
comes to mind. No idea how efficient it is though...
1 Comment
newacct
you can also write it as "all (
elem listx) input". @dlna: basically it expands to "all (\x -> x elem listx) input", which ensures that for every element of input, that it is an element of listxIs this homework? :)
You need to create one or two recursive functions to walk through both lists, and search for every string in the input.
Or, you could look up some good functions in the Prelude that helps here.
3 Comments
pier
yea, im new to haskell. I tried it out but I get an error. inputIndex :: [String] -> [String] -> Bool inputIndex [] _ = [] inputIndex listx input = [x
elem listx |x <- input] error: - Type error in explicitly typed binding *** Term : inputIndex *** Type : [String] -> [String] -> [a] *** Does not match : [String] -> [String] -> Boolnewacct
@dlna: your function is returning a list of Bools, one for each x. Whereas you just want one Bool, which is the logical and of all of them, so one thing you could do is "inputIndex listx input = and [x
elem listx |x <- input]"
Macke
Yup. There you are. 'and' is what you need to reduce [Bool] -> Bool.
One more way.
import Data.Set
(fromList input) `isSubsetOf` (fromList listX)
