CODEWITHSUNDEEP
c#linqgroup-byenumerable
Abbes omar
Abbes omar

Reputation: 51

GroupBy using a list of strings

This is my code

var y = tb.AsEnumerable()
          .GroupBy(r => new { pp1 = r[listView2.Items[0].Text], 
                              pp2 = r[listView2.Items[1].Text] })
          .Select(h => new { c1 = h.Key.pp1, 
                             c2 = h.Key.pp2, 
                             Total = h.Sum(s => s.Field<double>(listView3.Items[0].Text)) });

My problem is that I should GroupBy using listview items which contains the columns names that I will GroupBy But This code can only accept 2 items

Is there any way to GroupBy using a list of string ?

Upvotes: 2

Views: 355

Answers (1)

Servy
Servy

Reputation: 203820

You can use the following class to create a comparer that can compare sequences of items based on the values in those sequences, rather than based on the reference to the sequence:

public class SequenceComparer<T> : IEqualityComparer<IEnumerable<T>>
{
    private IEqualityComparer<T> comparer;
    public SequenceComparer(IEqualityComparer<T> comparer = null)
    {
        comparer = comparer ?? EqualityComparer<T>.Default;
    }
    public bool Equals(IEnumerable<T> x, IEnumerable<T> y)
    {
        return x.SequenceEqual(y, comparer);
    }

    public int GetHashCode(IEnumerable<T> sequence)
    {
        unchecked
        {
            int hash = 19;
            foreach (var item in sequence)
                hash = hash * 79 + comparer.GetHashCode(item);
            return hash;
        }
    }
}

Once we have this we can transform your grouping selector so that it projects out a sequence of the items you are interested in, since it's not known at compile time. The Select selector is largely unchanged.

var y = tb.AsEnumerable()
    .GroupBy(row => listView2.Items.Cast<ListViewItem>()
        .Select(item => row[item.Text]), new SequenceComparer<object>())
    .Select(group => new
    {
        Values = group.Key,
        Total = group.Sum(s => s.Field<double>(listView3.Items[0].Text)),
    });

Upvotes: 2

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