如果出现T的变化，则从List <T>中删除所有项目

Question

been struggling with this for a while now.

I'm dipping my toe in the WebAPI world and I have a List that can contains products with the same name but different prices. What I need to do is remove all references to a product is variations in price occur.

eg.
name = "Cornflakes" Price = "1.99M"
name = "Cornflakes" Price = "1.89M"
name = "Rice Krispies" Price = "2.09M"
name = "Cornflakes" Price = "2.09M"

No cornflakes should appear in my final list.

I've got the bulk written but it's removing the products too soon and I'm unsure where I should be removing them.

public IEnumerable<Product> GetProductsByCategory(int Id)
    {
        List<Product> sourceProductList = products.Where(p => p.CategoryID == Id).ToList();
        List<Product> tempProducts = new List<Product>();
        List<Product> targetProductList = new List<Product>();

        foreach (var product in sourceProductList)
        {
            bool isInTempList = tempProducts.Any(x => x.Name == product.Name);
            if (!isInTempList)
            {
                tempProducts.Add(product);
            }
            else
            {
                Product tempProduct = product;
                bool isPriceDifferent = tempProducts.Where(y => y.Name == tempProduct.Name).Any(y => y.Price != tempProduct.Price);
                if (isPriceDifferent)
                {
                    tempProducts.RemoveAll(p => p.Name == product.Name); 
                    // too soon as I may have lots of products with the same name
                    // but need to remove based on product.Name
                }
            }
        }
        targetProductList.AddRange(tempProducts);

        return targetProductList;
    }

Any help would be greatly appreciated.

Note: other cereals are available

Answer 1

Try this LINQ expression that will only select the products that have one distinct price:

var result = sourceProductList
    .GroupBy(x => x.Name)
    .Where(g => g.Select(x => x.Price).Distinct().Count() == 1)
    .Select(g => g.First());

See it working online: ideone .

Answer 2

Please try this:

class Program
    {
        static void Main(string[] args)
        {
            var list = new List<Product>
                {
                    new Product() {Name = "Cornflakes", Price = 100},
                    new Product() {Name = "Cornflakes", Price = 200},
                    new Product() {Name = "Rice Krispies", Price = 300},
                    new Product() {Name = "Cornflakes", Price = 400}
                };

            var uniqueItems = list.Where(w => (!list.Any(l=>l.Name.Equals(w.Name) && l != w)));

        }

        public class Product
        {

            public string Name { get; set; }
            public decimal Price { get; set; }
        }
    }

In the result you will have only one "Rice Krispies" item. I'm sure it will work faster than solution with GroupBy and Distinct, because we don't need to do these unnecessary things in your case.

Working Code - http://ideone.com/X8A3v

Answer 3

Something like this (freehand so may be slightly wrong syntax):

var toRemove = sourceProductList
    .GroupBy(p => p.Name)
    .Where(g => g.Count() > 1)
    .SelectMany(g => g)
    .GroupBy(p => p.Price)
    .Where(g => g.Count() > 1)
    .SelectMany(g => g.Select(p => p.ID))
    .Distinct()
    .ToList();
toRemove.ForEach(id => sourceProductList.RemoveAll(p => p.ID == id));

Answer 4

This should be as easy as grouping by name, getting only those where only 1 item exists in the groups:

var filtered = list.GroupBy(i => i.Name)
      .Where(i => i.Count() == 1)
      .SelectMany(x => x)

Live example: http://rextester.com/AUBOHU96105