Simple histogram generation of integer data in C#

Question

As part of a test bench I\'m building, I\'m looking for a simple class to calculate a histogram of integer values (number of iterations taken for an algorithm to solve a pro

Answer 1

You can use Linq:

var items = new[] {5, 6, 1, 2, 3, 1, 5, 2};
items
    .GroupBy(i => i)
    .Select(g => new {
        Item = g.Key,
        Count = g.Count()
    })
    .OrderBy(g => g.Item)
    .ToList()
    .ForEach(g => {
        Console.WriteLine("{0} occurred {1} times", g.Item, g.Count);
    });

Answer 2

You could use SortedDictionary

uint[] items = new uint[] {5, 6, 1, 2, 3, 1, 5, 2}; // sample data
SortedDictionary<uint, int> histogram = new SortedDictionary<uint, int>();
foreach (uint item in items) {
    if (histogram.ContainsKey(item)) {
        histogram[item]++;
    } else {
        histogram[item] = 1;
    }
}
foreach (KeyValuePair<uint, int> pair in histogram) {
    Console.WriteLine("{0} occurred {1} times", pair.Key, pair.Value);
}

This will leave out empty bins, though

Answer 3

My implementation of a simple extension method to create a histogram:

public static IReadOnlyDictionary<T, int> ToHistogram<T>(this IEnumerable<T> enumerable)
   => enumerable.GroupBy(item => item).ToDictionary(grouping => grouping.Key, grouping => grouping.Count());

Answer 4

Based on BastardSaint's suggestion I came up with a neat and fairly generic wrapper:

public class Histogram<TVal> : SortedDictionary<TVal, uint>
{
    public void IncrementCount(TVal binToIncrement)
    {
        if (ContainsKey(binToIncrement))
        {
            this[binToIncrement]++;
        }
        else
        {
            Add(binToIncrement, 1);
        }
    }
}

So now I can do:

const uint numOfInputDataPoints = 5;
Histogram<uint> hist = new Histogram<uint>();

// Fill the histogram with data
for (uint i = 0; i < numOfInputDataPoints; i++)
{
    // Grab a result from my algorithm
    uint numOfIterationsForSolution = MyAlorithm.Run();

    // Add the number to the histogram
    hist.IncrementCount( numOfIterationsForSolution );
}

// Report the results
foreach (KeyValuePair<uint, uint> histEntry in hist.AsEnumerable())
{
    Console.WriteLine("{0} occurred {1} times", histEntry.Key, histEntry.Value);
}

Took me a while to work out how to make it generic (to begin with I just overrode the SortedDictionary constructor which meant you could only use it for uint keys).