Pranay Rana

Explaining the important differences between the Event and Delegate patterns in C# and why they're useful.

In this post I am going to discuss about how to get distinct object using property of it from collection. Here I am going to show three different way to achieve it easily. In this post I am going to discuss about extension method that can do task more than the current Distinct method available in .Net framework. Distinct method of Linq works as following right now. public class Product { public string Name { get; set; } public int Code { get; set; } } Consider that we have product Class which is having Code and Name as property in it. Now Requirement is I have to find out the all product with distinct Code values. Product[] products = { new Product { Name = "apple", Code = 9 }, new Product { Name = "orange", Code = 4 }, new Product { Name = "apple", Code = 10 }, new Product { Name = "lemon", Code = 9 } }; var lstDistProduct = products.Distinct(); foreach (Product p in list1) { Console.WriteLine(p.Code + " : " + p.Name); } Output It returns all the product event though two product have same Code value. So this doesn't meet requirement of getting object with distinct Code value. Way 1 : Make use of MoreLinq Library First way to achieve the requirement is make use of MoreLinq Library, which support function called DistinctBy in which you can specify the property on which you want to find Distinct objects. Below code is shows the use of the function. var list1 = products.DistinctBy(x=> x.Code); foreach (Product p in list1) { Console.WriteLine(p.Code + " : " + p.Name); } Output As you can see in output there is only two object get return which actually I want. i.e. distinct value by Code or product. If you want to pass more than on property than you can just do like this var list1 = products.DistinctBy(a => new { a.Name, a.Code }); You can read about the MoreLinq and Download this DLL from here : http://code.google.com/p/morelinq/ one more thing about this library also contains number of other function that you can check. Way 2: Implement Comparable Second way to achieve the same functionality is make use of overload Distinct function which support to have comparator as argument. here is MSDN documentation on this : Enumerable.Distinct Method (IEnumerable, IEqualityComparer) So for that I implemented IEqualityComparer and created new ProductComparare which you can see in below code. class ProductComparare : IEqualityComparer { private Func _funcDistinct; public ProductComparare(Func funcDistinct) { this._funcDistinct = funcDistinct; } public bool Equals(Product x, Product y) { return _funcDistinct(x).Equals(_funcDistinct(y)); } public int GetHashCode(Product obj) { return this._funcDistinct(obj).GetHashCode(); } } So In ProductComparare constructor I am passing function as argument, so when I create any object of it I have to pass my project function as argument. In Equal method I am comparing object which are returned by my projection function. Now following is the way how I used this Comparare implementation to satisfy my requirement. var list2 = products.Distinct(new ProductComparare( a => a.Code )); foreach (Product p in list2) { Console.WriteLine(p.Code + " : " + p.Name); Output So this approach also satisfy my requirement easily. I not looked in code of MoreLinq library but I think its also doing like this only. If you want to pass more than on property than you can just do like this var list1 = products.Distinct(a => new { a.Name, a.Code });. Way 3: Easy GroupBy wa The third and most eaisest way to avoide this I did in above like using MoreLine and Comparare implementation is just make use of GroupBy like as below List list = products .GroupBy(a => a.Code ) .Select(g => g.First()) .ToList(); foreach (Product p in list) { Console.WriteLine(p.Code + " : " + p.Name); } In above code I am doing grouping object on basis of property and than in Select function just selecting fist one of the each group will doing work for me. Output So this approach also satisfy my requirement easily and output is similar to above two approach. If you want to pass more than on property than you can just do like this .GroupBy(a => new { a.Name, a.Code }). So this one is very easy trick to achieve the functionality that I want without using any thing extra in my code. Conclusion So Above is the way you can achieve Distinct of collection easily by property of object. Leave comment if you have any query or if you like it.

This small tip about how to show the negative currency value in your application. For Example if you have currency value like -1234 and you want to display it like -$1,234 according to you culture. Problem In C# to one of the way to format currency value easily is use ToString("c") with value will do work for you. For example check below code //format -1234 as currency.. Console.WriteLine((-1234).ToString("c")); Output This will display value in output like this ($1,234.00). But the actual problem with the formatting is its not displaying - sign with currency value. Solution So to come out of this You need to create a custom NumberFormatInfo from your current locale. Then you can specify it's CurrencyNegativePattern, for example: CultureInfo currentCulture = Thread.CurrentThread.CurrentCulture; CultureInfo newCulture = new CultureInfo(currentCulture.Name); newCulture.NumberFormat.CurrencyNegativePattern = 1; Thread.CurrentThread.CurrentCulture = newCulture; Console.WriteLine((-1234).ToString("c")); Output Now output of the above code is -$1,234.00. That's what actually needed display negative sign for negative currency value. So in above code actual trick done by NumberFormatInfo.CurrencyNegativePattern Property, which is set to 1 which associated with pattern -$n. There number of different pattern supported which you can check on MSDN and assign value to property according to your need. This will not affect positive value of currency i.e. if you pas 1234 as value its dispaly as $1,234 only. And for this this example my current culture is "en-US" . Conclusion I Hope you all like this simple and easy example of formatting negative currency. you can explore more on MSDN on reference provided at end of post. NumberFormatInfo Class - http://msdn.microsoft.com/en-us/library/system.globalization.numberformatinfo.aspx NumberFormatInfo.CurrencyNegativePattern Property - http://msdn.microsoft.com/en-us/library/system.globalization.numberformatinfo.currencynegativepattern.aspx