在逗号分隔列表中查找字符串值

Question

I have a list(string) with members in the form of 'label,location'; labels are distinct. I need a method which accepts a label parameter and returns a location.

I can iterate through using foreach to find the correct label, then manipulate the list member using Split to return the location. However I'm sure there's a better way, presumably using LINQ, along the lines of

return theList.Single(x => x == theLabel);

This doesn't work however since the list values == label,location.

Answer 1

See the code below:

string get_location(List<string> list, label)
{
  return list.Select(s => s.Split(',')).ToDictionary(s => s[0], s => s[1])[label];
}

If there are multiple requests on the same list, then it is better to save that dictionary and then reuse for all labels queried:

var map = list.Select(s => s.Split(',')).ToDictionary(s => s[0], s => s[1]);

Alternatively:

var map = new Dictionary<string, string>();
list.ForEach(s => { var split = s.Split(','); map.Add(split[0], split[1]); });

Answer 2

Since the labels are unique, you might consider converting your data to a dictionary<string,string> . You can keep the label as the key and location as the value .

var lableLocatonDict = theList.Select(item => item.Split(','))
                                      .ToDictionary(arr => arr[0], arr => arr[1]);

Now to access a location(value) for a specific label(key) you can simply do this

var location = lableLocatonDict["LabelToCheck"];

You can use the ContainsKey method if you want to check whether an item exists in the dictionary before accessing it.

if(lableLocatonDict.ContainsKey("LabelToCheck"))
{
    var location = lableLocatonDict["LabelToCheck"];
}

Or the TryGetValue

var location = string.Empty;
if(lableLocatonDict.TryGetValue("LabelToCheck",out location))
{
   // location will have the value here             
}

Answer 3

As I and the other 2 answers recommend, Dictionary was designed for exactly this purpose. You expressed concern with iterating a dict as opposed to a list thinking it could be more difficult, but in fact it is easier since no splitting would be needed (and faster).

Dictionary<String,String> locations = new Dictionary<String,String>();

//How to add locations
locations.Add("Sample Label","Sample Location");

//How to modify a location
locations["Sample Label"] = "Edited Sample Locations";

//Iterate locations
foreach (var location in locations)
{
    Console.WriteLine(location.key);
    Console.WriteLine(location.value);
}

I would even go a bit further and say to future proof your application and add the ability for more information to be stored in each location, you should really be using ObservableCollection<T> where T is a custom class object:

public class LocationInfo
{
    String Label {get;set;}
    String Location {get;set;}
    String Description {get;set;}
}

ObservableCollection<LocationInfo> Locations = new ObservableCollection<LocationInfo>();