LINQ GroupBy

fpoyavo
fpoyavo used Ask the Experts™
on
Hi Experts,

I need your help to add grouping by T.tid   in this code. Thank you in advance.


                    var mydata = db.data
                   
                    .Where(T => T.some.Any(F => F.my_id == another_id))
                   
                    .ToArray()
                 
                    .Select(T => new MyInfo
                    {
                        TId = T.tid,
                        PData = T.data
                       
                     
                    }).ToArray();
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Fernando SotoRetired
Distinguished Expert 2017

Commented:
Hi fpoyavo;

What is the data type of T.tid? Because if you create a grouping it will return a hierarchical data object. What is also the data type of MyInfo.Tid? Because it will need to store that object.

Can you show in a diagram what you want that grouping to look like or what you need it to look like.

Author

Commented:
T.tid is int. MyInfo.Tid is int. MyInfo.PData is string.
Fernando SotoRetired
Distinguished Expert 2017

Commented:
So what are you trying to accomplish by grouping in the query?
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Author

Commented:
To eliminate duplicated data
Fernando SotoRetired
Distinguished Expert 2017

Commented:
Grouping will not get rid of duplicates. When you say duplicates does that mean that all columns having the same values or certain columns only.

Author

Commented:
Some of them. Not all.
Retired
Distinguished Expert 2017
Commented:
Hi fpoyavo;

The IEqualityComparer below is used to see if two rows in the database table can be considered duplicates. The IEqualityComparer is only considering two columns to test whether they are considered duplicates or not. If more columns are needed to determine  if they are duplicate then you must add those columns as well.

// See comment below
var ec = new OrderEqualityComparer();

// In the query you need to add the Distinct method after the first ToArray.
var mydata = db.data
               .Where(T => T.some.Any(F => F.my_id == another_id))
               .ToArray()
               .Distinct(ec)
               .Select(T => new MyInfo
               {
                   TId = T.tid,
                   PData = T.data              
               }).ToArray();

// This class is used to match two data object from the database table
// data to see if they are considered duplicates.               
class OrderEqualityComparer : IEqualityComparer<data>
{

    public bool Equals(data d1, data d2)
    {
        if (d1.TID == d2.TID & d1.OtherCoulmn == d2.OtherCoulmn)
        {
            return true;
        }
        else
        {
            return false;
        }
    }


    public int GetHashCode(data d)
    {
        int hCode = d.TID.GetHashCode() ^ d.OtherCoulmn.GetHashCode();
        return hCode.GetHashCode();
    }

}

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