Convert list to dictionary using linq and not worrying about duplicates

Here's the obvious, non linq solution:

foreach(var person in personList)
{
  if(!myDictionary.ContainsKey(person.FirstAndLastName))
    myDictionary.Add(person.FirstAndLastName, person);
}

If you don't mind always getting the last one added, you can avoid the double lookup like this:

foreach(var person in personList)
{
    myDictionary[person.FirstAndLastName] = person;
}

LINQ solution:

// Use the first value in group
var _people = personList
    .GroupBy(p => p.FirstandLastName, StringComparer.OrdinalIgnoreCase)
    .ToDictionary(g => g.Key, g => g.First(), StringComparer.OrdinalIgnoreCase);

// Use the last value in group
var _people = personList
    .GroupBy(p => p.FirstandLastName, StringComparer.OrdinalIgnoreCase)
    .ToDictionary(g => g.Key, g => g.Last(), StringComparer.OrdinalIgnoreCase);

If you prefer a non-LINQ solution then you could do something like this:

// Use the first value in list
var _people = new Dictionary<string, Person>(StringComparer.OrdinalIgnoreCase);
foreach (var p in personList)
{
    if (!_people.ContainsKey(p.FirstandLastName))
        _people[p.FirstandLastName] = p;
}

// Use the last value in list
var _people = new Dictionary<string, Person>(StringComparer.OrdinalIgnoreCase);
foreach (var p in personList)
{
    _people[p.FirstandLastName] = p;
}

A Linq-solution using Distinct() and and no grouping is:

var _people = personList
    .Select(item => new { Key = item.Key, FirstAndLastName = item.FirstAndLastName })
    .Distinct()
    .ToDictionary(item => item.Key, item => item.FirstFirstAndLastName, StringComparer.OrdinalIgnoreCase);

I don't know if it is nicer than LukeH's solution but it works as well.