CODEWITHSUNDEEP
listhaskell
Amber
Amber

Reputation: 275

How can I get multiple nth elements in a list?

I want to know how I can get multiple elements in a list in one function

for example if I wanted to get elements 1 2 3 and 4 from list a, I would have to type a!!0 ++ a!!1 ++ a!!2 ++ a!!3. This takes up a lot of space especially if the list name is more than one character. so I'm wondering if I can do something like a!![0,1,2,3] instead and get all of those elements in a much shorter way. Thank you.

Upvotes: 1

Views: 502

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476594

You can work with a mapping where you lookup all items for a list, so:

map (a !!) [0,1,2,3]

If you are however interested in the first four items, you can work with take :: Int -> [a] -> [a]:

take 4 a

especially since looking up by an index (with (!!)) is not a common operation in Haskell: this is unsafe since it is not guaranteed that the index is in bounds. Most list processing is done with functions like take, drop, sum, foldr, etc.

Upvotes: 5

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