Compare/count values in a System.Collections.ArrayList

Question

I'm scrubbing 5 files for a specific value. I dont anticipate any different values, BUT since this is for my own educational purposes, I would like the application to count, compare and print the most popular value.

for example:

ArrayList arrName = new ArrayList();
arrName.Add("BOB")
arrName.Add("JOHN")
arrName.Add("TOM")
arrName.Add("TOM")
arrName.Add("TOM")

The result I would like is going to be TOM but being a novice, I really dont know how to move forward.

Any thoughts, suggestions or examples are greatly appreciated. Thank you.

Answer 1

You can use a Dictionary (.NET 2.0+) to hold the repeated count of each value:

Dictionary<string, int> counts = new Dictionary<string, int>();
foreach (string name in arrName) {
   int count;
   if (counts.TryGetValue(name, out count)) {
      counts[name] = count + 1;
   } else {
      counts.Add(name, 1);
   }
}

// and then look for the most popular value:

string mostPopular;
int max = 0;
foreach (string name in counts.Keys) {
   int count = counts[name];
   if (count > max) {
       mostPopular = name;
       max = count;
   }
}

// print it
Console.Write("Most popular value: {0}", mostPopular);

If you're using C# 3.0 (.NET 3.5 +) then use:

var mostPopular = (from name in arrName.Cast<string>()
                   group name by name into g
                   orderby g.Count() descending
                   select g.Key).FirstOrDefault();

Console.Write("Most popular value: {0}", mostPopular ?? "None");