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haskelllist-comprehension

How do you solve this Haskell problem?

I want to define a function replicate to replicate a list of numbers by its value using only list comprehension, for example:

replicate [5,1,3,2,8,1,2]
output: [5,5,5,5,5,1,3,3,3,2,2,8,8,8,8,8,8,8,8,1,2,2]

I know this would be easy to use the 'replicate' built in function but only list comprehension is allow, how can I do this?

THANKS!

Solution

  • Neat little problem. I solved it like this.

    replicate list = [ a | a <- list, _ <- [1..a]]

    Prelude> replicate [5,1,3,2,8,1,2]

    [5,5,5,5,5,1,3,3,3,2,2,8,8,8,8,8,8,8,8,1,2,2]

    It takes each value in the list, creates that many copies of itself, and then moves to the next value.