C# Advanced String Manipulation or LINQ - How To

Question

I am not sure how to go about this. I have a dynamic comma delimited string:

A - B, Hello, C - D, World

I need to take that string and remove/filter out all instances of items that have a " - " in it. So the desired result would be a new string that would look like this:

Hello, World

Now if this cannot be done using string manipulation, the string comes from a

IEnumerable<string>

using linq. So maybe there is a way to get my desired result by using LINQ.

Here is the code:

var apps = lbAppGroup.Items.Cast<ListItem>().Where(i => i.Selected).Select(i => i.Value);
string selectedAppValues = String.Join(", ", apps.ToArray());

This returns my initial example.

I am using C# 3.5. Any direction or examples would be greatly appreciated!

Answer 1

Just do it with LINQ like you're already doing:

var apps = lbAppGroup.Items.Cast<ListItem>().Where(i => i.Selected && !i.Value.Contains("-")).Select(i => i.Value);
string selectedAppValues = String.Join(", ", apps.ToArray());

Also, you could use a regular expression like this:

Regex re = new Regex("(?<=[,^]\s*)[^-]+(?=[,$])");

But you would only do that if you only had the string.

Answer 2

This will return all strings in a sequence that do not contain a dash:

apps.Where(s => !s.Contains("-"));

you can chain your LINQ statements so you can either add it to the select like this:

var apps = lbAppGroup.Items.Cast<ListItem>().Where(i => i.Selected).Where(s => !s.Contains("-")).Select(i => i.Value);

or use it in the next statement:

string selectedAppValues = String.Join(", ", apps.Where(s => !s.Contains("-")).ToArray());

Answer 3

Personally, I have an extension method

// takes any IEnumerable, not just strings (like an int array for example)
public static string Join(this IEnumerable source, string delimiter = ", ")
{
   return string.Join(
            delimiter, 
            source.OfType<object>()
            .Select(i => i == null ? "null" : i.ToString()).ToArray()
           )
}

If you really want to go LINQ all the way

lbAppGroup.Items.Cast<ListItem>().Where(i => i.Selected)
.Where(i => i.Value.Contains("-"))
.Select(i => i.Value).Aggregate((x, y) => x + ", " + y);

For really large collections this won't perform as well as string.Join though.

Answer 4

I cant comment in LINQ particullary, but I can tell you how i'd go about manipulating this string.

"A - B, Hello, C - D, World"

If each string is seperated by a comma, then each string is an item in a list of strings.

The first step is to parse out each item. Add each character, starting from the beginning, to a seperate string. Once you hit a comma, add this string to a string array, clear the string, and move to the next character (Or next character after the space). Like so:

Begin   -> ""
[0] = A -> "A"
[1] =   -> "A "
[2] = - -> "A -"
...
[5] = , -> "A - B"
list<string>.add("A - B")

Once you have the list of strings, you then iterate through the list and say

if (list.get(x).contains("-") list.remove(x)

Or whatever.

Now that this is all set up, you can just hack off the whole list stuff and just do it on the fly: 1. Determine "current" item 2. If it has - in it, do not add it to the final string 3. Otherwise, add it with the comma 4. Move to next item and repeat until finished