Dynamically create anonymous object from list values c#

Question

I have a list (or can be array) of strings that I want to dynamically create an anonymous object from. How do I do this?

var dataSet = new DataSet();
dataSet         


        

Answer 1

Stripping down your question, what you want is to be able to group a list of items based on a runtime property which could be composed of one or more properties of that item. In essence, it means you need a selector function (which is your Key method) that transforms an item into a key.

In order for GroupBy to work, it needs to be able to compare any two instances of the key to see if they're equal. This means the key needs to implement a meaningful Equals() method, or you need an IEqualityComparer implementation that does the work for you. In this case I wouldn't bother with creating a new Key, just write an Equality Comparer that can compare two DataRows directly:

var duplicates = dataTable
        .AsEnumerable()
        .GroupBy(r => r, new MyDataRowComparer(keys))
        .Where(c => c.Count() > 1)
        .ToList();


internal class MyDataRowComparer : IEqualityComparer<DataRow>
{
    private readonly string[] _keys;

    public MyDataRowComparer(string[] keys)
    {
        _keys = keys; // keep the keys to compare by.
    }

    public bool Equals(DataRow x, DataRow y)
    {
        // a simple implementation that checks if all the required fields 
        // match. This might need more work.
        bool areEqual = true;
        foreach (var key in _keys)
        {
            areEqual &= (x[key] == y[key]);
        }
        return areEqual;
    }

    public int GetHashCode(DataRow obj)
    {
        // Add implementation here to create an aggregate hashcode.
    }
}