Lambda Functions in .Net

Lambda expressions in .Net are denoted by the ‘=>’ symbol.

These powerful operators can be used to create sleek, optimized loops that perform much faster.

The usage below condenses the equivalent of at least 20 lines of two loops.

(Sorry kiddos, no time for VB conversion…C# only this time. ;))

Edit (20101229): Lambda rocks! Simply amazing! Greatest ever!

Ex. 1:

            PaymentMethodCollection visiblePaymentMethods = new PaymentMethodCollection();

            DataSet myPaymentMethods = GlobalDataLoads.PaymentMethods();
            List<DataRow> pmids = myPaymentMethods.Tables[0].Select("Visible = 1").ToList();
            List<int> ids = pmids.Select(i => i["PaymentMethodId"]).Cast<int>().ToList(); 
            List<PaymentMethod> pm = availablePaymentMethods.FindAll(i => ids.Contains(i.PaymentMethodId));


Ex. 2:

USER user = tol_dc.USERs.Single(u => u.USER_ID == (int)userid);

Ex. 3:

//DataContext tol_dc;
            List<int> courseids = registrationList.Select(i=>i.MODULE_ID).ToList();
            List<MODULE> modulenames = tol_dc.MODULEs.Where(i=>courseids.Contains(i.MODULE_ID)).Cast<MODULE>().ToList();

Ex. 4: (Get the value of data item inside the child repeater of a parent repeater if the UID is known)

//RepeaterCommandEventArgs e
        if ((stringvalueineed==null) || (stringvalueineed=="")) {
        int uid= (int)((System.Data.DataTable)rptCourses.DataSource).Rows[e.Item.ItemIndex]["UID"];
        stringvalueineed= ((System.Data.DataRow[])(((Repeater)rptOne.Items[e.Item.ItemIndex].FindControl("rptTwo")).DataSource)).Single(i => (int)i["UID"] == uid)["COLUMNNAME"].ToString();

Ex. 5a: (filter a list of available products by removing all excluded products from the list, such as those out of stock)

        private bool Load_AvailableProducts()
            string region = Session["region"];

            LinqData.DataClassesDataContext dc = new LinqData.DataClassesDataContext();

            List<LinqData.GET_PRODUCT_LISTResult> allproducts = (from p in dc.GET_PRODUCT_LIST(region)
                                       select p).ToList();
            List<int> excproducts = (from ListItem m in lbExcludedProducts.Items
                                       select Convert.ToInt32(m.Value)).ToList();

            List <LinqData.GET_PRODUCT_LISTResult> availproducts = allproducts.Where(p => !excproducts .Contains(p.ProductID)).ToList();

            lbAvailableProducts.DataSource = availproducts;

            lbAvailableProducts.DataTextField = "ProductName";
            lbAvailableProducts.DataValueField = "ProductID";
            return true;

Ex. 5b: (same as this version code is smaller and more load is placed on SQL server rather application (IIS). analyze with SQL profiler and you’ll see the difference)

        private bool Load_AvailableProducts()
            string region = Session["Region"];

            LinqData.DataClassesDataContext dc = new LinqData.DataClassesDataContext();

            List<LinqData.GET_PRODUCT_LISTResult> availproducts = (from i in dc.GET_PRODUCT_LIST(region)
                                       select i).Where(m => !(from ListItem l in lbExcludedProducts.Items
                                       select Convert.ToInt32(l.Value)).ToList().Contains(m.ProductID)).ToList();

            lbAvailableProducts.DataSource = availproducts;

            lbAvailableProducts.DataTextField = "ProductName";
            lbAvailableProducts.DataValueField = "ProductID";
            return true;

The lambda one-liner indicated in the snippet below essentially nests at least two “for/foreach” loops. See my related article here for full source.

Ex. 6:

protected void LoadFactories()

        if (ddlSegment.SelectedIndex > 0)
            using (AndroneticsDataContext db = new AndroneticsDataContext(
                List<UP_GET_FactoriesResult> allFactories = db.UP_GET_Factories(Convert.ToInt32(ddlRegion.SelectedValue), null).ToList();

                ////this would be approximately how you would approach traditionally
                //foreach (UP_GET_FactoriesResult r in allFactories)
                //    if (GetUnregisteredRobots(r.FACTORY_ID).Count != 0)
                //    {
                //        //etc, would need another loop here
                //    }

                //now for the lambda way
                var Factories = allFactories.Where(
                    r => GetUnregisteredRobots(r.FACTORY_ID).Where(
                        ra => !lstDecommissionRobots.Items.Contains(new ListItem(ra.ROBOT_NAME,ra.ROBOT_ID.ToString()))).Count() != 0);

                ddlFactories.DataSource = Factories;
                ddlFactories.DataTextField = "FACOTRY_TITLE";
                ddlFactories.DataValueField = "FACTORY_ID";

                ListItem li = new ListItem("", "");
                ddlFactories.Items.Insert(0, li);

    private List<UP_LOAD_COURSE_RobotsResult> GetUnregisteredRobots(int courseid)
        using (AndroneticsDataContext db = new AndroneticsDataContext(
            List<UP_LOAD_COURSE_RobotsResult> allRobots = db.UP_LOAD_COURSE_Robots(courseid).ToList();

            int userID = int.Parse(Request.QueryString["ID"]);
            List<string> excregisteredRobots = (from m in db.UP_GET_REGISTERED_Robots(userID) select m.MODULE_NAME).ToList();

            return allRobots.Where(m => !excregisteredRobots.Contains(m.MODULE_NAME)).ToList();

Ex. 7 (foreach)

//make sure list first
List<mydatatype> data = ReturnSomeData().ToList();

//technically long way but helps understand what is happening
Func<mydatatype, string> f = (a) => a.somepropertyname = "somevalue";
                    data.ForEach(i => f(i));

//or simply

data.ForEach(c => c.somepropertyname = "somevalue";

Ex. 8 Lambda Cast to Custom Object (list of objects from one type to another)

//DAL.StoreProcedures is simply a static class with functions that instantiate and dispose of datacontexts and return object collections from data calls

List<geocode> geocodes = DAL.StoredProcedures.LoadGeoCodes_Zip(market, datestart).Select(g=> new geocode {lat=g.Latitude.ToString(),lng=g.Longitude.ToString()}).Cast<geocode>().ToList();

MSDN, “Lambda Expressions (C# Programming Guide)”,
MSDN C# Developer Center, “101 Linq Samples”,
Fraction of The Blogosphere,

About Ronnie Diaz

Ronnie Diaz is a software engineer and tech consultant. Ronnie started his career in front-end and back-end development for companies in ecommerce, service industries and remote education. This work transitioned from traditional desktop client-server applications through early cloud development. Software included human resource management and service technician workflows, online retail e-commerce and electronic ordering and fulfillment, IVR customer relational systems, and video streaming remote learning SCORM web applications. Hands on server experience and software performance optimization led to creation of a startup business focused on collocated data center services and continued experience with video streaming hardware and software. This led to a career in Amazon Prime Video where Ronnie is currently employed, building software and systems which stream live sports and events for millions of viewers around the world.

Posted on December 21, 2010, in Programming & Development and tagged , , , , , , , , , , , , , , , , , , , , , , , , , . Bookmark the permalink. 1 Comment.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: