如何使用Linq在列表中找到属性值不同的第一项？

Question

I have an ordered list of objects, and I would like to find the index of each item where a property changes, and get a dictionary/list of pairs matching index to property. For example, finding the index of each new first letter in a list of words ordered alphabetically.

I can do this with a foreach loop:

Initials = new Dictionary<char, int>();
int i = 0;
foreach (var word in alphabeticallyOrderedList))
{
    if (!Initials.ContainsKey(word.First()))
    {
        Initials[word.First()] = i;
    }
    i++;
}

But I feel like there should be an elegant way of doing this with Linq.

Answer 1

You could have the same functionality with LINQ by using the overload of Select that exposes the index and by using GroupBy + ToDictionary :

 Initials = alphabeticallyOrderedList
    .Select((word, index) => new { Word = word, WordIndex = index })
    .GroupBy(x => x.Word[0])
    .ToDictionary(charGroup => charGroup.Key, charGroup => charGroup.First().WordIndex);

But to quote myself:

LINQ is not always more readable, especially when indexes are important. You also lose some debugging, exception handling and logging capabilities if you use a large LINQ query