How to search in 2D array by LINQ ?[version2]

Question

I have an 2D array like this:

string[,] ClassNames =
{
  {"A","Red"},
  {"B","Blue"},
  {"C","Pink"},
  {"D","Green"},
  {"X","Black"},
};

i search ClassName in 1nd column by for statement and return ColorName in 2nd column like this:

string className = "A";
string color = "Black";
for (int i = 0; i <= ClassNames.GetUpperBound(0); i++)
{
   if (ClassNames[i, 0] == className)
   {
      color = ClassNames[i, 1];
      Response.Write(color);
      break;
   }
}

i want use LINQ instead of for statement to get the color by className. how to convert above for statement to LINQ.

2D array is in fact a `c` stuff, in c# we should use other collection structure/classes. — King King, Sep 07 '13 at 13:41

p.s.w.g · Accepted Answer · 2013-09-07T13:49:03.770

You can do use the Enumerable.Range method to generate a sequence of integers, and then use Linq to query over that.

Something like this would work:

string color = Enumerable
    .Range(0, ClassNames.GetLength(0))
    .Where(i => ClassNames[i, 0] == className)
    .Select(i => ClassNames[i, 1])
    .FirstOrDefault() ?? "Black";

Or in query syntax:

string color = 
    (from i in Enumerable.Range(0, ClassNames.GetLength(0))
     where ClassNames[i, 0] == className
     select ClassNames[i, 1])
    .FirstOrDefault() ?? "Black";

Or perhaps convert the array to a Dictionary<string, string> first:

Dictionary<string, string> ClassNamesDict = Enumerable
    .Range(0, ClassNames.GetLength(0))
    .ToDictionary(i => ClassNames[i, 0], i => ClassNames[i, 1]);

And then you can query it much more easily:

color = ClassNamesDict.ContainsKey(className) 
      ? ClassNamesDict[className] 
      : "Black";

Generating the dictionary first and then querying it will be far more efficient if you have to do a lot of queries like this.

@SamieyMehdi That's the [null coalescing operator](http://msdn.microsoft.com/en-us/library/ms173224.aspx). It basically means 'if the value to the left is null, use the value to the right instead'. Note that this only works for reference or nullable types. If your actual array is a `int[,]`, you'll have to cast the result to a `(int?)` in the select clause to get that to work. — p.s.w.g, Sep 07 '13 at 13:48

score 3 · Answer 2 · answered Sep 07 '13 at 13:37

Here you are:

color = ClassNames.Cast<string>()
                  .Select((x, i) => new { x, i })
                  .GroupBy(x => x.i / 2, (k,x) => x.Select(y => y.x))
                  .Where(g => g.First() == className)
                  .Select(x => x.Last()).First();

But to be honest, I would never use LINQ to do that. It's less efficient, less readable and worse to maintain. You should consider using your existing for loops or change your data structure, to be List<CustomClass> or Dictionary<string, string> instead of string[,].

You'll get that error when there is no element matching. I've tested it with your sample input and returned `"Red"`. — MarcinJuraszek, Sep 07 '13 at 13:50

How to search in 2D array by LINQ ?[version2]

2 Answers2

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