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Find Duplicates Using LINQ
How can we find duplicate occurrences of values in a collection? I will demonstrate this here using a collection of cities. City class looks like this:
public class City
{
public string Name { get; set; }
public string Country { get; set; }
}
Cities collection is initialised with this code:
List<City> cities =
new List<City>
{
new City{ Name = "Sydney", Country = "Australia" },
new City{ Name = "Sydney", Country = "Australia" },
new City{ Name = "New York", Country = "USA" },
new City{ Name = "Paris", Country = "France" },
new City{ Name = "Milan", Country = "Spain" },
new City{ Name = "Melbourne", Country = "Australia" },
new City{ Name = "Auckland", Country = "New Zealand" },
new City{ Name = "Tokyo", Country = "Japan" },
new City{ Name = "New Delhi", Country = "India" },
new City{ Name = "Hobart", Country = "Australia" },
new City{ Name = "Boston", Country = "USA"}
};
Objective is to find countries which occur more than once in the collection and while I am doing that I would also like to know the number of cities for that country. To do this I can use this query. I am using a foreach loop to output my results.
var query =
from c in cities
group c by c.Country into g
where g.Count() > 1
select new { Country = g.Key, CityCount = g.Count()};
foreach (var item in query)
{
Console.WriteLine("Country {0} has {1} cities", item.Country, item.CityCount);
}
By running the above query I get this output which is correct as there are only two countries in the collection which have more than one city.
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August 16th, 2008 at 10:39 pm
Good article. Thanks for sharing!