string.split for alternating characters in c#

Question

I know this is going to be an easy answer but I am new to C#. There is a lot of answers on for different types of splits, but I cannot find one for this problem. I am trying to split a string into two by alternating characters.

The example would be: string example = "stackoverflow" and the output would be "sakvrlo" and "tcoefo" .

If it is an odd number of characters it does not matter if the two new strings are of different lengths.

Thanks!

Answer 1

StringBuilder sb1 = new StringBuilder();
StringBuilder sb2 = new StringBuilder();

string source = "some string to split";

// ALTERNATE: if you want an explicitly typed char[]
// char[] source = "some string to split".ToCharArray();

for( int i = 0; i < source.Length; i++ )
{
   if( i % 2 == 0 )
   {
        sb1.Append( source[i] );
   }
   else
   {
        sb2.Append( source[i] );
   } 
}

Notes:

• There is no BCL method that I am aware of that does this automatically (eg string.SplitAlternating() .

• Since the size of the string is known, the StringBuilders can be initialized with a fixed buffer size.

• LINQ solution (@usr's answer) is cleaner but slower (if it matters, which is probably rarely).

• If performance truly does matter, the fastest way is probably to obtain a pointer to the start of the original char array and iterate by incrementing two separate pointers created by two char arrays declared using stacalloc . Subsequently, those two char arrays can then be passed as an argument to string's constructor. Make sure to append null terminators.

Answer 2

var a = new string(source.Where((c,i) => i % 2 == 0).ToArray());
var b = new string(source.Where((c,i) => i % 2 != 0).ToArray());