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c#.netstringlist
chwi
chwi

Reputation: 2802

Combine and append elements in List<string> C# .NET

I have a List of strings

List<string> myList = new List<string>();

myList.Add(string1_1);
myList.Add(string1_2);
myList.Add(string2_1);
myList.Add(string2_2);
myList.Add(string3_1);
myList.Add(string3_2);

Now, after some magic, I want to combine the elements of the List, making them like this

myList[0] = string1_1 + string1_2
myList[1] = string2_1 + string2_2
myList[2] = string3_1 + string3_2

thus also cutting the size of the List in half. How can this be achieved?

Upvotes: 0

Views: 1391

Answers (3)

Flea777
Flea777

Reputation: 1022

You could try something like this:

var half = myList
           .Select((s,idx) => s + (idx < myList.Count() - 1 ? myList[idx +1] : string.Empty) )
           .Where((s,idx) => idx % 2 == 0)
           .ToList();

You can do a projection of all items in the form string[i] + string[i+1] (being careful to check that the string[i+1] element exists):

.Select((s,idx) => s + (idx < myList.Count() - 1 ? myList[idx +1] : string.Empty) )

Then filter only the even elements:

.Where((s,idx) => idx % 2 == 0)

Upvotes: 1

Trevor Elliott
Trevor Elliott

Reputation: 11252

A simple for loop would work:

List<string> inputList = new List<string>();
List<string> outputList = new List<string>();

for (int i = 0; i < inputList.Count; i += 2) // assumes an even number of elements
{
    if (i == inputList.Count - 1)
        outputList.Add(inputList[i]); // add single value
        // OR use the continue or break keyword to do nothing if you want to ignore the uneven value.
    else
        outputList.Add(inputList[i] + inputList[i+1]); // add two values as a concatenated string
}

For loops are good for looping and dealing with pairs or triplets of elements at a time.

Upvotes: 6

MarcinJuraszek
MarcinJuraszek

Reputation: 125660

I would definitely go with a for loop approach provided by Trevor, but if you'd like to do it using LINQ you can use GroupBy and string.Join:

myList = myList.Select((x, i) => new { x, i })
               .GroupBy(x => x.i / 2)
               .Select(g => string.Join("", g.Select(x => x.x)))
               .ToList();

Upvotes: 6

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