CODEWITHSUNDEEP
c#linqlambda
hardywang
hardywang

Reputation: 5172

Append index number to duplicated string value in a list - by using Lambda

I have a IList<string>() which holds some string values, and there could be duplicated items in the list. What I want is to append a index number to end of the string to eliminate the duplication.

For example, I have these values in my list: StringA, StringB, StringC, StringA, StringA, StringB. And I want the result looks like: StringA1, StringB1, StringC, StringA2, StringA3, StringB2. I need to retain the original order in list.

Is there a way I can just use one Lambda expression?

Upvotes: 0

Views: 127

Answers (3)

Selman Gen&#231;
Selman Gen&#231;

Reputation: 101701

You are looking for something like this:

yourList.GroupBy(x => x)
        .SelectMany(g => g.Select((x,idx) => g.Count() == 1 ? x : x + idx))
        .ToList();

Edit: If the element order matters, here is another solution:

var counts = yourList.GroupBy(x => x).ToDictionary(x => x.Key, x => x.Count());

var values = counts.ToDictionary(x => x.Key, x => 0);

var list = yourList.Select(x => counts[x] > 1 ? x + ++values[x] : x).ToList();

Upvotes: 4

Jodrell
Jodrell

Reputation: 35716

This uses some lambda expressions and linq to do it, maintaining the order but I'd suggested a function with a foreach loop and yield return would be better.

var result = list.Aggregate(
        new List<KeyValuePair<string, int>>(),
        (cache, s) =>
        {
            var last = cache.Reverse().FirstOrDefault(p => p.Key == s);
            if (last == null)
            {
                cache.Add(new KeyValuePair<string, int>(s, 0));
            }
            else
            {
                if (last.Value = 0)
                {
                    last.Value = 1;
                }

                cache.Add(new KeyValuePair<string, int>(s, last.Value + 1));
            }

            return cache;
        },
        cache => cache.Select(p => p.Value == 0 ? 
            p.Key :
            p.Key + p.Value.ToString()));

Upvotes: 0

Habib
Habib

Reputation: 223282

You can do:

List<string> list = new List<string> { "StringA", "StringB", "StringC", "StringA", "StringA", "StringB" };
var newList =
    list.Select((r, i) => new { Value = r, Index = i })
    .GroupBy(r => r.Value)
    .Select(grp => grp.Count() > 1 ?
                grp.Select((subItem, i) => new
                {
                    Value = subItem.Value + (i + 1),
                    OriginalIndex = subItem.Index
                })
                : grp.Select(subItem => new
                {
                    Value = subItem.Value,
                    OriginalIndex = subItem.Index
                }))
    .SelectMany(r => r)
    .OrderBy(r => r.OriginalIndex)
    .Select(r => r.Value)
    .ToList();

and you will get:

StringA1,StringB1,StringC,StringA2,StringA3,StringB2

If you don't want to preserve order then you can do:

var newList = list.GroupBy(r => r)
                .Select(grp => grp.Count() > 1 ? 
                           grp.Select((subItem, i) => subItem + (i + 1))
                           : grp.Select(subItem => subItem))
                .SelectMany(r => r)
                .ToList();

Upvotes: 0

Related Questions