格式/按条件分组的字符串列表

Question

I have a question regarding formatting List of strings. I'm looping through dictionary of two strings: value and tagname.

myList.Add(myDict.Keys.ElementAt(n) + ":" + myDict.Values.ElementAt(n).Value);

When the iteration is done, I need to format that string as follows:

for (int tmp = 0; tmp < myList.Count; tmp++)
{
    if (tmp < myList.Count - 1)
    {
        tempString += String.Format(myList[tmp].ToString() + " ,");
    }
}

Output of that tempstring will be like this: TagName: Value, TagName: Value, TagName: Value. But here's the tricky part (for me): several tag names are the same, and for the program purposes, these items which have same tag name needs to be grouped by that tag name, something like this: TagName: value, TagName: value, value, value Do you have any suggestions for this?

Update (reading XML):

    var evt = (from el in doc.Descendants("test")
       where el.Parent.Name == "Event_1"
       group el by el.Parent.Element("NameOfEvent").Value into g
       select new {
           Name = g.Key,
           Tests = g.Select(x => new {
               Value = x.Element("value").Value,
               TagName = x.Element("tagName").Value
           })
       }).FirstOrDefault();

     Console.WriteLine("Event name: " + evt.Name);
     foreach (var test in evt.Tests)
     {

     }

Answer 1

It looks like you need a combination of LINQ's Group By and String.Join .

Group By takes a list of objects and produces a list of lists of objects where each list's objects all contain something in common.

{"Key1", "Value1"},
{"Key2", "Value2"},
{"Key1", "Value3"}

Becomes

{
   {"Key1", "Value1"},
   {"Key1", "Value3"}
},
{
   {"Key2", "Value2"},
}

When you group all of the values by their values. Then you can just take that result and join the values in a comma separated list using String.Join .

What you want to do is construct a list that contains all of your values grouped together under the same key and then join them into a string.

There are 3 steps to do this:

1. Group value by tag
2. Construct a string for each of the values for each tag
3. Construct the final string from each of the other constructed strings

Which would look something like this:

// Your keys and values
List<KeyValuePair<string, string>> dict = new List<KeyValuePair<string, string>>
{
    new KeyValuePair<string, string>("TagName1", "value1"),
    new KeyValuePair<string, string>("TagName2", "value2"),
    new KeyValuePair<string, string>("TagName1", "value3")
};

// 1. Group all of the values together based on the key
IEnumerable<IGrouping<string, KeyValuePair<string, string>>> groupedValues = 
            dict.GroupBy(v => v.Key);

// 2. Construct a string for each of the groups
IEnumerable<string> builtValues = groupedValues.Select(group =>
{
    // returns "TagName1:value1, value2" etc.
    return group.Key + ":" + string.Join(", ", group.Select(g => g.Value));
});

// 3. Construct the final string from each of the constructed strings
string finalResult = string.Join(", ", builtValues);

Then finalResult would contain TagName1:value1, value3, TagName:value2 , which seems to be relatively what you want.