Intersection of two data table return zero rows with custom Data Comparer

Question

I want to get all common rows (including duplicate rows) between two data table having more than 45000 rows.

However, I want to skip "Column 2" and "all columns after column 6" out of comparison scope.But I am getting no rows as intersection result. Could any one suggest me where I am doing wrong?

Here's my code written:

CustomDataRowComparer myDRComparer = new CustomDataRowComparer();
var commonData = outputTable.AsEnumerable().Intersect(prevTable.AsEnumerable(), myDRComparer).CopyToDataTable();



   public class CustomDataRowComparer : IEqualityComparer<DataRow>
    {
        public bool Equals(DataRow x, DataRow y)
        {
            for (int i = 0; i < 7; i++)
            {


                if (i !=1) // Don't want to consider this column for comparison
                {
                    if (x[i].ToString() != y[i].ToString())
                    {
                        return false;
                    }
                }

            }
            return true;
        }

        public int GetHashCode(DataRow obj)
        {
            return obj.ToString().GetHashCode();
        }

I think the hash is wrong. Try this : return string.Join("^",obj.ItemArray.Select((x,i) => i == 1 ? "" : x.ToString()).ToArray()).GetHashCode(); — jdweng
– jdweng, Commented Jul 21, 2016 at 11:10
I just realized if you use my hash the Equals() method can just compare DataRow x to DataRow y the hash will be unique and will determine where rows match. — jdweng
– jdweng, Commented Jul 21, 2016 at 11:19

jdweng · Accepted Answer · 2016-07-21 11:23:56Z

1

Here is full code

    public class CustomDataRowComparer : IEqualityComparer<DataRow>
    {
        public bool Equals(DataRow x, DataRow y)
        {
            return x.Equals(y);
        }

        public int GetHashCode(DataRow obj)
        {
            return string.Join("^", obj.ItemArray.Select((x, i) => i == 1 ? "" : x.ToString()).ToArray()).GetHashCode();
        }
    }

answered Jul 21, 2016 at 11:23

jdweng

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7 Comments

Raj Over a year ago

How can I adapt lambda expression to exclude two more columns? Right now, You are excluding i=1. Can we adapt it to exclude i>=7 ?

Raj Over a year ago

I adjusted my data table so that I have 6 columns in beginning that I would like to consider for comparison and I changed the return statement as 'return string.Join("^", obj.ItemArray.Select((x, i) =>i>5? "" : x.ToString()).ToArray()).GetHashCode();' But it's not working still.

jdweng Over a year ago

Are you getting back any rows that compare? Try comparing the same datatable table against itself to see if the code works. All rows should be returned.

Raj Over a year ago

If I compare same data table, it works fine and return all rows. But it's not working when I am comparing it to another table.It return zero row. However, another table has equal rows if we ignore column 2 value and columns values after column 6.

jdweng Over a year ago

Try : (i == 1) || (i >= 5) ?

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