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I have an array of Products, a custom POCO. Some of these products refer to the same item. Some will have the TariffUnrestricted price and another will have the StandingChargePenceDay . I need to merge these together.

I am trying to group the products together, then select out the key and the values for each product. I think the code will explain better:

public override Product[] Import(string path, Func<Worksheet, bool> worksheetSelector = null)
    Product[] products = base.Import(path, worksheetSelector);

    var groups = products.GroupBy(p => new Product
        PlanName = p.PlanName,
        RateType = p.RateType,
        ContractDuration = p.ContractDuration,
        Duration = p.Duration,
        TariffDescription = p.TariffDescription,
        //TariffUnrestricted = p.TariffUnrestricted,
        //StandingChargePenceDay = p.StandingChargePenceDay

    products = groups.Select(g =>
        Product product = g.Key;
        product.TariffUnrestricted = g.Max(p => p.TariffUnrestricted);
        product.StandingChargePenceDay = g.Max(p => p.StandingChargePenceDay);
        return product;

    return products;

The items do not merge. The number of groups is always the same as the number of products (1:1).

I tried making the Product IComparable<Product>, IComparer<Product>, IEquatable<Product> but nothing works?

My google-fu is week. I cannot find the correct terms :C

What am I doing wrong?


1 solution

Why are you trying to group by a new product? All that will do is attempt to group by the reference value itself, won't it? Which would explain the 1:1 correlation between groups and products. :laugh:
Don't you want something like:
var groups = products.GroupBy(p => p.TariffDescription);
or similar?

A quick test:
public class MyClass
    public int Value { get; set; }
    public string Name { get; set; }

List<MyClass> list = new List<MyClass>();
MyClass a = new MyClass() { Value = 1, Name = "A" };
MyClass b = new MyClass() { Value = 1, Name = "B" };
MyClass c = new MyClass() { Value = 2, Name = "C" };
MyClass d = new MyClass() { Value = 2, Name = "D" };
MyClass e = new MyClass() { Value = 3, Name = "E" };
var g1 = list.GroupBy(m => m.Value);
var g2 = list.GroupBy(m => new MyClass { Value = m.Value, Name = m.Name });
Console.WriteLine(g1.Count() + ":" + g2.Count());

Gives "3:5"

Adding the IEquatable interface doesn't change that either:
public class MyClass : IEquatable<MyClass>
    public int Value { get; set; }
    public string Name { get; set; }
    public bool Equals(MyClass other)
        return Value == other.Value;
I still get 3:5

Andy Lanng 7-Jan-16 12:19pm
But what's wrong with grouping by the ref value? is it a restriction?
OriginalGriff 7-Jan-16 12:24pm
There's nothing *wrong* with it - it's just that they will all by definition be different... :laugh:
Andy Lanng 7-Jan-16 12:26pm
Hmm, I /think/ I get it, but I thought that IEquatable meant that I was dictating that they /are/ the same.

It works with new instead of Product. Wouldn't that have the same issue O_o
OriginalGriff 7-Jan-16 12:47pm
Doesn't look like it - I just tried a quick test and modified the answer
OriginalGriff 7-Jan-16 12:50pm
Just added a quick mod to my test:
var g2 = list.GroupBy(m => new MyClass { Value = m.Value, Name = m.Name } .Value);
That gives "3:3" with or without the IEquatable interface.
Andy Lanng 8-Jan-16 4:01am
I'm sure there is a way, but using an anon class works fine. Thanks for taking a look ^_^

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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