'How do I remove every third character from a string in c# If I don't know what character it is?

This code should remove every third character and the last character from the String Data variable without the code knowing what characters the String Data contains.

The problem is that this code works well if the length of the String Data is 3 characters, but if it is more, then the characters to be deleted will not be deleted.

If I replace x == Data.Length with x == 3, then I get a runtime error if I run the code with more than three characters in the String Data variable.

int x = 0;

for (int i = 0; i < Data.Length; i++)
{
    x++;
    if (x == Data.Length - i) //3
    {
        Data = Data.Remove(i, i - 1);
        Data = Data.Remove(Data.Length - 1);
        x = 0;
    }
}
c++sharpstringfor-loop


Solution 1:[1]

You can accumulate the required characters into a StringBuilder, then chop off the last one:

string datum = "123456789";

var sb = new System.Text.StringBuilder();

for (int i = 0; i < datum.Length; i++)
{
    if (i % 3 != 2)
    {
        sb.Append(datum[i]);
    }
}

sb.Length--; // Remove last char
datum = sb.ToString();

Console.WriteLine(datum);

Outputs:

12457

The way a StringBuilder works internally is more efficient than repeatedly concatenating to a string.

Solution 2:[2]

You can try to use lambda Where with your logic which will get an IEnumerable<char> then passing in string construct method get the result.

var result = Data.Where((x,i)=> i%3 != 2 && i != Data.Length -1).ToArray();
Data = new string(result);

Solution 3:[3]

You could take advantage of .Chunk(), which lets you split up your string in chunks of (in your scenario) three chars, and of .SkipLast(), which lets you skip the last char in each chunk. In the end, join all chars to create your output string.

var output = string.Join(string.Empty, 
    input.Chunk(3).SelectMany(ch => ch.SkipLast(1)));

The input

var input = "12345678901234567890123456789";

will produce

1245780134679023568

Both .Chunk() and .SkipLast() are found in the System.Linq namespace.

Example fiddle here.

Solution 4:[4]

Does this help?

for (int i = 0; i < Data.Length; i++)
{
    if((i+1)%3==0)
    {
        Data = Data.Remove(i, 1);
    }
}

Solution 5:[5]

I'd suggest using Linq Where() combined with the remainder operator to gather the chars that are at index 1 or 2, 4 or 5, etc:

var Data = "123456789abcdef";
Data = string.Join("", Data.Where((c, i) => (i+1) % 3 > 0));

Working .NET Fiddle: https://dotnetfiddle.net/DlSiiY

Solution 6:[6]

Another one using a List<char> and going backwards:

string input = "1234567890";
List<char> values = new List<char>(input.ToCharArray());
values.RemoveAt(values.Count - 1);
for(int i=(values.Count-1); i>=0;  i--)
{
    if ((i+1) % 3 == 0)
    {
        values.RemoveAt(i);
    }
}
string output = new string(values.ToArray());

Console.WriteLine(" input: " + input);
Console.WriteLine("output: " + output);

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1
Solution 2 D-Shih
Solution 3 Astrid E.
Solution 4 Peter Mourfield
Solution 5 Peter B
Solution 6 Idle_Mind

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