Alternative to if, else if

Question

I have a lot of if, else if statements and I know there has to be a better way to do this but even after searching stackoverflow I\'m unsure of how to do so in my particular cas

Answer 1

To avoid the blatant Schlemiel the Painter's approach that looping over all the keys would involve: let's use regular expressions!

// a dictionary that holds which bill text keyword maps to which provider
static Dictionary BillTextToProvider = new Dictionary {
    {"SWGAS.COM", "Southwest Gas"},
    {"georgiapower.com", "Georgia Power"}
    // ...
};

// a regex that will match any of the keys of this dictionary
// i.e. any of the bill text keywords
static Regex BillTextRegex = new Regex(
    string.Join("|", // to alternate between the keywords
                from key in BillTextToProvider.Keys // grab the keywords
                select Regex.Escape(key))); // escape any special characters in them

/// If any of the bill text keywords is found, return the corresponding provider.
/// Otherwise, return null.
string GetProvider(string billText) 
{
    var match = BillTextRegex.Match(billText);
    if (match.Success) 
        // the Value of the match will be the found substring
        return BillTextToProvider[match.Value];
    else return null;
}

// Your original code now reduces to:

var provider = GetProvider(txtvar.BillText);
// the if is be unnecessary if txtvar.Provider should be null in case it can't be 
// determined
if (provider != null) 
    txtvar.Provider = provider;

Making this case-insensitive is a trivial exercise for the reader.

All that said, this does not even pretend to impose an order on which keywords to look for first - it will find the match that's located earliest in the string. (And then the one that occurs first in the RE.) You do however mention that you're searching through largeish texts; if .NET's RE implementation is at all good this should perform considerably better than 200 naive string searches. (By only making one pass through the string, and maybe a little by merging common prefixes in the compiled RE.)

If ordering is important to you, you might want to consider looking for an implementation of a better string search algorithm than .NET uses. (Like a variant of Boyer-Moore.)