C# How to place a comma after each word but the last in the list

Question

I totally new to C# and learning as I go. I am stuck on issue which I'm hoping an experienced programmer can help. I have added a CheckedListBox to my form and added a collection of 6 items to it. I need all but the last item selected to have a comma placed beside it, so my question is: how can I tell C# NOT to place a comma beside the last item selected?

foreach (object itemChecked in RolesCheckedListBox.CheckedItems)
{
    sw.Write(itemChecked.ToString() + ",");
}

Thanks for any help received! Dan

Answer 1

It can be done using string.Join() method:

string commaSeparated = string.Join(",", 
                RolesCheckedListBox.CheckedItems.Select(item => item.ToString());

For example:

string[] names = new []{ "a", "b"};
string separatedNames = string.Join(",", names);

Will result that separatedNames will be "a,b"

Answer 2

Here are some articles I wrote about this problem:

http://blogs.msdn.com/b/ericlippert/archive/2009/04/13/restating-the-problem.aspx

http://blogs.msdn.com/b/ericlippert/archive/2009/04/15/comma-quibbling.aspx

The comments to the second article have dozens of solutions to a slightly harder version of the problem; it is educational to browse those solutions and see which ones you find elegant and which ones you find gross.

Answer 3

A way to enhance your example could be:

var index = 0;
foreach (object itemChecked in RolesCheckedListBox.CheckedItems)
{
    if ( index>0 ) sw.Write( "," );
    sw.Write(itemChecked.ToString());
    index++;
}

Not elegant, but working.

Answer 4

您可以使用Join函数而不是循环：

sw.Write(string.Join(",", RolesCheckedListBox.CheckedItems));

Answer 5

在4.0中，您可以简单地使用string.Join（字符串分隔符，IEnumerable值）为所有非空值调用ToString（）方法：

var commaSeparated = string.Join(",", RolesCheckedListBox.CheckedItems);

Answer 6

1. transform your ListItemCollection to a string array using linq
2. use String.Join

Like:

public string ItemsToString(ListItemCollection items)
{
    string[] stringArray = (from ListItem item in items where item.Selected select item.ToString()).ToArray();
    return String.Join(", ", stringArray);
}

you could use it by

sw.Write(ItemsToString(RolesCheckedListBox.CheckedItems));

Or if you prefer a single line for the job:

sw.Write(String.Join(", ", (from ListItem item in RolesCheckedListBox.CheckedItems select item.ToString()).ToArray()));

Answer 7

In .Net 4 you can use static String.Join<T> Method (String, IEnumerable<T>) and print concatenated string.

Otherwise the easy way is to prepend comma to all elements but the first one:

bool shouldPrependComma = false;
foreach (object itemChecked in RolesCheckedListBox.CheckedItems) 
{
  if (shouldPrependComma) sw.Write(",");
  sw.Write(itemChecked.ToString());
  shouldPrependComma = true;
}

Answer 8

foreach (object itemChecked in RolesCheckedListBox.Items)
            {
                if (itemChecked != RolesCheckedListBox.Items[RolesCheckedListBox.Items.Count - 1])
                    sw.Write(itemChecked.ToString() + ",");
            }

That should help you. Also, I just used "Items", you used CheckedItems. Change all instances of Items to CheckedItems if you want to only iterate through checked items.

Answer 9

Jon Skeet为这类问题实施了SmartEnumerable 。