Question

How much less efficent would the linq technique be in the following case and could either be optimised?

Linq technique:

public String FindProviderName(Int32? TrueName)
{
    String providerName = (from p in this.Providers
                           where p.TrueName == TrueName
                           select p.ProviderName).First().ToString();

    return providerName;
}

Walking technique:

public String FindProviderName(Int32? TrueName)
{
    String providerName = String.Empty;

    foreach (IProvider provider in this.Providers)
    {
        if (provider.TrueName == TrueName)
        {
            providerName = provider.ProviderName;
            break;
        }
    }

    return providerName;
}

Answer 1

If that is LINQ-to-objects, they’ll both be pretty fast. If you want faster, consider a Dictionary<int,string> and use TryGetValue(...). Obviously you need to pre-generate the dictionary, perhaps via ToDictionary().

Note that the two examples shown are different when there is no match; one throws; one returns an empty string. Also, there is no need to call ToString() on a string.

---

Re the faster version (comments); you need a field,

Dictionary<int,string> lookup;

And at some point prior to use (or after data changes) you need to populate it:

lookup = providers.Where(p => p.RealName != null)
    .ToDictionary(p => p.RealName.Value,
        p => p.ProviderName);

Then your lookup would be like:

string providerName;
if(realName == null ||
    !lookup.TryGetValue(realName.Value, out providerName))
    return null;
return providerName;