Question

My goal is to run through a database of strings and get the count each time each substring occurs. In other words I need to extract all possible word combinations from the string.

For example the input might be "this is the first string".

I would want to extract "this is", "is the", "the first", "first string", "this is the", "is the first", "the first string", "this is the first", "is the first string".

I only need to go left to right, always in order.

I am not really sure where to start with this. I already have the code to read database and save into list, just need to know how to extract all possible sub strings based on the space character.

Answer 1

The following method builds up a list of the indices of all spaces in your string (plus notional start and end spaces), then returns the substring between every ordered pair of indices:

static IEnumerable<string> SpaceDelimitedSubstrings(string input)
{
    List<int> indices = new List<int> { -1 };
    int current = -1;
    while ((current = input.IndexOf(' ', current + 1)) > -1)
    {
        indices.Add(current);
    }
    indices.Add(input.Length);

    int minLength = 1;
    for (int i = 0; i < indices.Count - minLength; i++)
        for (int j = i + minLength; j < indices.Count; j++)
            yield return input.Substring(indices[i] + 1, indices[j] - indices[i] - 1);
}

Called as follows

string input = "this is the first string";
foreach (var s in SpaceDelimitedSubstrings(input))
{
    Console.WriteLine(s);
}

it gives

Changing minLength to 2 will cut out the single-word returns.