Excluding words from dictionary

Question

I am reading through documents, and splitting words to get each word in the dictionary, but how could I exclude some words (like "the/a/an").

This is my function:

private void Splitter(string[] file)
{
    try
    {
        tempDict = file
            .SelectMany(i => File.ReadAllLines(i)
            .SelectMany(line => line.Split(new[] { ' ', ',', '.', '?', '!', }, StringSplitOptions.RemoveEmptyEntries))
            .AsParallel()
            .Distinct())
            .GroupBy(word => word)
            .ToDictionary(g => g.Key, g => g.Count());
    }
    catch (Exception ex)
    {
        Ex(ex);
    }
}

Also, in this scenario, where is the right place to add .ToLower() call to make all the words from file in lowercase? I was thinking about something like this before the (temp = file..):

file.ToList().ConvertAll(d => d.ToLower());

Answer 1

Do you want to filter out stop words?

 HashSet<String> StopWords = new HashSet<String> { 
   "a", "an", "the" 
 }; 

 ...

 tempDict = file
   .SelectMany(i => File.ReadAllLines(i)
   .SelectMany(line => line.Split(new[] { ' ', ',', '.', '?', '!', }, StringSplitOptions.RemoveEmptyEntries))
   .AsParallel()
   .Select(word => word.ToLower()) // <- To Lower case 
   .Where(word => !StopWords.Contains(word)) // <- No stop words
   .Distinct()
   .GroupBy(word => word)
   .ToDictionary(g => g.Key, g => g.Count());

However, this code is a partial solution: proper names like Berlin will be converted into lower case: berlin as well as acronyms: KISS (Keep It Simple, Stupid) will become just a kiss and some numbers will be incorrect.

Answer 2

I would do this:

var ignore = new [] { "the", "a", "an" };
tempDict = file
    .SelectMany(i =>
        File
            .ReadAllLines(i)
            .SelectMany(line =>
                line
                    .ToLowerInvariant()
                    .Split(
                        new[] { ' ', ',', '.', '?', '!', },
                        StringSplitOptions.RemoveEmptyEntries))
                    .AsParallel()
                    .Distinct())
    .Where(x => !ignore.Contains(x))
    .GroupBy(word => word)
    .ToDictionary(g => g.Key, g => g.Count());

You could change ignore to a HashSet<string> if performance becomes an issue, but it would be unlikely since you are using file IO.