Reduce a list into smaller lists of two using LINQ (Functional Programming)

Question

Hey guys, I'm trying to get my head around LINQ and FP, so forgive me if this is naive. I'm trying to do some string parsing using LINQ and mapping onto a function, so I need to split my string up into smaller strings.

I want to split the array up into smaller lists of two. Can I use a reduce (.Aggregate()) to do this? I was trying to work out how to apply the reduce to return a list but I wasn't having any luck.

What I want is:

myString.ToCharArray().Take(2)

Mapped onto every second element.I couldn't get around in my head how to reduce the list without applying the take to every single element, instead of every second one.

Concrete example.

given (1, 2, 3, 4, 5, 6)

I want ((1, 2), (3,4), (5, 6))

To clarify:

given "abcdef"

I want "ab", "cd", "ef"

Cheers for your help guys.

Answer 1

Enumerable.Range(0, myString.Length)
      .GroupBy(index => index / 2, index => myString[index])
      .Select(eachGroup => new string(eachGroup.ToArray()));

Note that the example above relies on the fact that you have index based access to the collection. To make it work on every IEnumerable<T> without this limitation:

collection.Select((e,i) => new { Index = i, Element = e })
      .GroupBy(x => x.Index / 2, x => x.Element);

Answer 2

This doesn't seem like the approach your looking for, but it's what I see:

Enumerable.Range(0, myString.Length - 1)
    .Where(i => i % 2 == 0)
    .Select(i => myString.Substring(i, 2).ToCharArray());

Note: I think if you have an odd number of characters the substring will probably crash; Probably have to add a check and use something like (myString.Length % 2 == 0 ? 2 : 1), but I haven't tested.

Second Note: To me the difficulty here is that your Reduce actually depends on the array index rather than the values; Hence my solution of enumerating the array indexes and working from there. Another solution would be to provide a method (I can't think of one built in) that enumerates the characters in the string using a tuple that contains the index and the character.