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Short solution for short problems

Using LINQ to concatinate an object property from a list of objects

Just put this in a little demo to make it clear. I created a simple object Person, with ID, FirstName and LastName.

Now I fill a List with 3 persons (later I'll fill it with 20000 to do a performance check):

List<Person> persons = newList<Person>();

{

    newPerson(){ID=0, FirstName="Mark", LastName="Deraeve"},

    newPerson(){ID=1, FirstName="Priscilla", LastName="Lauwerijssen"},

    newPerson(){ID=2, FirstName="Anne-Lisa", LastName="Deraeve"}

};

Instead of looping over the list and concatinating it, like this:

start = DateTime.Now;

foreach (Person p in persons)

{

    sPersons = String.Format("{0},{1}", sPersons, p.FirstName);

}

//remove front ,

Console.WriteLine("With Loop: " + sPersons);

I can also just use 1 line to accomplisch this:

Console.WriteLine("With LINQ: " +string.Join(",", persons.Select(p => p.FirstName)));

Result:

 

Now let's say you do not want all records, this makes it even more easy, just put a Where before the Select and you got it!

Let's only show person named 'Deraeve':

Console.WriteLine("With LINQ: " +string.Join(",", persons.Where(p => p.LastName == "Deraeve").Select(p => p.FirstName)));

Result:

 

Now last, lets try to see performance difference. I'll fill the list with 20000 persons. This is where the power comes in. (The number 188889 or 188890(+1 for the extra comma) is the length of the result string)

 

Amazingly, the LINQ only uses 3 or 4 milliseconds, the old for loop takes 1-3 (There is a difference when using String.Format (slower) or just "string + ','+ "string") seconds. This can really make a big difference in today's apps.

So here the complete code so you can test it yourself:

Code of the console app:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

 

namespace TestConsoleApp

{

    classProgram

    {

        staticvoid Main(string[] args)

        {

            List<Person> persons = newList<Person>();

            /*{

                new Person(){ID=0, FirstName="Mark", LastName="Deraeve"},

                new Person(){ID=1, FirstName="Priscilla", LastName="Lauwerijssen"},

                new Person(){ID=2, FirstName="Anne-Lisa", LastName="Deraeve"}

            };*/

 

            for (int i = 0; i < 20000; i++)

            {

                persons.Add(newPerson() { ID = i, FirstName = string.Format("Name{0}", i), LastName = "Deraeve" });

            }

 

            string sPersons="";

            DateTime start = DateTime.Now;

            TimeSpan ts;

 

            start = DateTime.Now;

            sPersons = string.Join(",", persons.Select(p => p.FirstName));

            ts = DateTime.Now.Subtract(start);

            Console.WriteLine("With LINQ: " + sPersons.Length);

            Console.WriteLine(String.Format("Seconds:{0} Miliseconds{1} ", ts.Seconds, ts.Milliseconds));

            Console.WriteLine("");

 

            sPersons = "";

 

            start = DateTime.Now;

            sPersons = string.Join(",", persons.Where(p => p.LastName == "Deraeve").Select(p => p.FirstName));

            ts = DateTime.Now.Subtract(start);

            Console.WriteLine("With LINQ and Where: " + sPersons.Length);

            Console.WriteLine(String.Format("Seconds:{0} Miliseconds{1} ", ts.Seconds, ts.Milliseconds));

            Console.WriteLine("");

 

            sPersons="";

 

            start = DateTime.Now;

            foreach (Person p in persons)

            {

                sPersons = String.Format("{0},{1}", sPersons, p.FirstName);

            }

            ts = DateTime.Now.Subtract(start);

 

            Console.WriteLine("With for loop: " + sPersons.Length);

            Console.WriteLine(String.Format("Seconds:{0} Miliseconds{1} ",ts.Seconds,ts.Milliseconds));

            Console.WriteLine("");

 

            sPersons = "";

 

            start = DateTime.Now;

            foreach (Person p in persons)

            {

                if (p.LastName == "Deraeve")

                {

                    sPersons = String.Format("{0},{1}", sPersons, p.FirstName);

                }

            }

 

            ts = DateTime.Now.Subtract(start);

 

            Console.WriteLine("With for loop and if: " + sPersons.Length);

            Console.WriteLine(String.Format("Seconds:{0} Miliseconds{1} ", ts.Seconds, ts.Milliseconds));

            Console.WriteLine("");

 

            sPersons = "";

 

            start = DateTime.Now;

            foreach (Person p in persons)

            {

                sPersons = sPersons + ',' + p.FirstName;

            }

            ts = DateTime.Now.Subtract(start);

 

            Console.WriteLine("With for loop without format: " + sPersons.Length);

            Console.WriteLine(String.Format("Seconds:{0} Miliseconds{1} ", ts.Seconds, ts.Milliseconds));

            Console.WriteLine("");

 

            Console.ReadKey();

        }

    }

}

Code of the Person class:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

 

namespace TestConsoleApp

{

    publicclassPerson

    {

        publicstring FirstName { get; set; }

 

        publicstring LastName { get; set; }

 

        publicint ID { get; set; }

 

    }

}

Things even get better for the Join statement when we add the last name to the result:

sPersons = string.Join(",", persons.Where(p => p.LastName == "Deraeve").Select(p => p.FirstName + ' ' + p.LastName));

VS

foreach (Person p in persons)

{

    sPersons = String.Format("{0},{1} {2}", sPersons, p.FirstName, p.LastName);

}


Result: 




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