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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?

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();

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();

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()));

Make every string unique by appending counter

I have a list of string and I want to make every string in that list unique by appending a number at the end of it. Also, it is case insensitive, so "apple" should be assumed the SAME as "Apple" or "apPlE"
For example:
List<string> input = new List<string>();
input.Add("apple");
input.Add("ball");
input.Add("apple");
input.Add("Apple");
input.Add("car");
input.Add("ball");
input.Add("BALL");
Expected output:
"apple", "ball", "apple2", "Apple3", "car", "ball2", "BALL3"
I need help to develop the logic to produce the output. Thank you.
Edited: I CANNOT have 0 and 1, the repeated string must start with 2, 3, 4...

var newList = input.GroupBy(x => x.ToUpper())
.SelectMany(g => g.Select((s, i) => i == 0 ? s : s + (i+1)))
.ToList();
var str = String.Join(", ", newList);
EDIT
var newList = input.Select((s, i) => new { str = s, orginx = i })
.GroupBy(x => x.str.ToUpper())
.Select(g => g.Select((s, j) => new { s = j == 0 ? s.str : s.str + (j + 1), s.orginx }))
.SelectMany(x => x)
.OrderBy(x => x.orginx)
.Select(x => x.s)
.ToList();

Selecting array values from specific indexes order by index array

I want to select array values from specific indexes
Now I have this.
var xs = new[] { 11,12,13,14,15 };
var ind = new[] { 3,2,1,0 };
var results = xs.Where((x, idx) => ind.Contains(idx)).ToArray();
The result is {11,12,13,14}
However, I want my result to be ordered by index array which should be {14,13,12,11}
Thank you very much

var results = ind.Select(i => xs[i]).ToArray();

var array = xs.Zip(ind, (x, i) => new Tuple<int, int>(x, i))
.OrderBy(t => t.Item2)
.Select(t => t.Item1)
.ToArray();

Checking a dictionary if there are same values for a key

I have a dictionary object like this:
CustomKeys<int, string>
eg;
1000, F1
1001, F2
1002, F1
1003, F4
1004, F2
I want to know if I have more than 1 of same values in this dictionary. I would also want to keep a note of which keys(unique id) has duplicates.
Is that possible?

It is possible using GroupBy and than Count() > 1 to keep track of which values that have duplicates.
var q = dic.GroupBy(x => x.Value)
.Select (x => new { Item = x, HasDuplicates = x.Count() > 1 });

You can find all key values they had the same values like this;
Dictionary<int, string> d = new Dictionary<int, string>();
d.Add(1000, "F1");
d.Add(1001, "F2");
d.Add(1002, "F1");
d.Add(1003, "F4");
d.Add(1004, "F2");
var dublicate = d.ToLookup(x => x.Value, x => x.Key).Where(x => x.Count() > 1);
foreach (var i in dublicate)
{
Console.WriteLine(i.Key);
}
Here is a DEMO.
But if you want to get a boolean value since your item's has a same value, look at Magnus's answer which is great.

I'm not sure by what you mean by "keeping note of which has duplicate values". If you mean keeping note of the keys, you could do this:
var keys = new Dictionary<int, string>();
keys.Add(1000, "F1");
keys.Add(1001, "F2");
keys.Add(1002, "F1");
keys.Add(1003, "F4");
keys.Add(1004, "F2");
var duplicates = keys.GroupBy(i => i.Value).Select(i => new
{
keys = i.Select(x => x.Key),
value = i.Key,
count = i.Count()
});
foreach (var duplicate in duplicates)
{
Console.WriteLine("Value: {0} Count: {1}", duplicate.value, duplicate.count);
foreach (var key in duplicate.keys)
{
Console.WriteLine(" - {0}", key);
}
}
If you mean keeping track of the duplicate values only, see Sonor's answer.

Another solution could be:
var duplicates = dictionary.GroupBy( g => g.Value )
.Where( x => x.Count( ) > 1 )
.Select( x => new { Item = x.First( ), Count = x.Count( ) } )
.ToList( );

create a dictionary using 2 lists using LINQ

I am trying to create a dictionary from 2 lists where one list contains keys and one list contains values. I can do it using for loop but I am trying to find if there is a way of doing it using LINQ.
Sample code will be helpfull. Thanks!!!!

In .NET4 you could use the built-in Zip method to merge the two sequences, followed by a ToDictionary call:
var keys = new List<int> { 1, 2, 3 };
var values = new List<string> { "one", "two", "three" };
var dictionary = keys.Zip(values, (k, v) => new { Key = k, Value = v })
.ToDictionary(x => x.Key, x => x.Value);

List<string> keys = new List<string>();
List<string> values = new List<string>();
Dictionary<string, string> dict = keys.ToDictionary(x => x, x => values[keys.IndexOf(x)]);
This of course assumes that the length of each list is the same and that the keys are unique.
UPDATE: This answer is far more efficient and should be used for lists of non-trivial size.

You can include the index in a Select expression to make this efficient:
var a = new List<string>() { "A", "B", "C" };
var b = new List<string>() { "1", "2", "3" };
var c = a.Select((x, i) => new {key = x, value = b[i]}).ToDictionary(e => e.key, e => e.value );
foreach (var d in c)
Console.WriteLine(d.Key + " = " + d.Value);
Console.ReadKey();

var dic = keys.Zip(values, (k, v) => new { k, v })
.ToDictionary(x => x.k, x => x.v);

You can use this code and working perfectly.
C# Code:
var keys = new List<string> { "Kalu", "Kishan", "Gourav" };
var values = new List<string> { "Singh", "Paneri", "Jain" };
Dictionary<string, string> dictionary = new Dictionary<string, string>();
for (int i = 0; i < keys.Count; i++)
{
dictionary.Add(keys[i].ToString(), values[i].ToString());
}
foreach (var data in dictionary)
{
Console.WriteLine("{0} {1}", data.Key, data.Value);
}
Console.ReadLine();
Output Screen: