How to create comma separated string value if key matches in dictionary<string, string>?

I have a string[] as below. Basically, this contains a set of filters and I want to separate them with a key. Key can be duplicate and if this happens then add comma separated value.

What is the best approach to that? Is any other alternative to Dictionary? If there is, then I am open for it.

Input:

var input = new List<string>
{
    "Location=COL&StockNumber=1111150416",
    "Location=NYC&StockNumber=2222250416&Invoice=Part",
    "Location=NYC&StockNumber=2222250416&Invoice=Part&Supplier=AutoZone"
};

Expected Output:

var output = new Dictionary<string, string>
{
    { "Location", "(COL, NYC)" },
    { "StockNumber", "(1111150416, 2222250416, 2222250417)" },
    { "Invoice", "(Part)" },
    { "Supplier", "(AutoZone)" }
};

Issues

• If key already exists, then throws an error. Want to add bracket and comma separated value.

Code:

var testDictionary = new Dictionary<string, string>();
for(var i = 0; i < keys.Count; i++) {
    var items = keys[i].Split("&");

    for (var j = 0; j < items.Length; j++)
    {
        var data = items[j].Split("=");
        if (testDictionary.ContainsKey(data[0]))
         {
            testDictionary[data[0]] = // ADD Comma separated value here but not sure how to do that.
         }
        testDictionary.Add(data[0], data[1]);
    }
}

>Solution :

I suggest Linq query:

Given

var input = new List<string> {
   "Location=COL&StockNumber=1111150416",
   "Location=NYC&StockNumber=2222250416&Invoice=Part",
   "Location=NYC&StockNumber=2222250416&Invoice=Part&Supplier=AutoZone"
};

We can get the required dictionary as (Fiddle)

using System.Linq;

...

var output = input
  .SelectMany(line => line.Split('&'))
  .Select(item => item.Split('='))
  .GroupBy(pair => pair[0], pair => pair[1])
  .ToDictionary(group => group.Key, 
                group => $"({string.Join(",", group.Distinct())})");

What’s going on:

1. We split each string by & and flatten the enumeration. Now we have enumeration of "Key=Value" strings
2. We split each "Key=Value" by = into an arrays pair
3. We group by pair[0] (which will be Key) pair[1]s which will be values
4. We Join Distinct values for each Key
5. Finally, we materialize the result as Dictionary