How can I Pass in a lambda that will be used as a filter for a row in a datatable?

Question

I've got some code which accepts a DataTable as a parameter and calculates the total of several of the columns in the DataTable. I thought it might be nice to be able to pass in a lambda expression which would perform a filter on the column I'm totaling.

Here's a portion of the code:

public TrafficTotals CalculateTotals(DataTable table)
{
    TrafficTotals total = new TrafficTotals();
    total.TotalTraffic = table.AsEnumerable().Sum(p => p.Field<int>("Converted"));
    // More stuff

I can manually add a filter into the expression directly in the code:

var filteredTotal = table.AsEnumerable().Where(p => p.Field<string>("MyColumn") == "Hello").Sum(p => p.Field<int>("Converted"));

But instead I'd like to pass the "Where" portion as lambda expression instead, but I keep getting lost in the syntax to get the parameters correct.

I have several ways of working around this that don't really involve lambdas but it seems like a nice way of handling this.

Any ideas?

Answer 1

I'm slightly confused because you're already specifying the Where clause with a lambda expression, but I suspect you want this:

public TrafficTotals CalculateTotals(DataTable table, 
                                     Func<DataRow, bool> filter)
{
    TrafficTotals total = new TrafficTotals();
    total.TotalTraffic = table.AsEnumerable()
                              .Where(filter)
                              .Sum(p => p.Field<int>("Converted"));
    // More stuff
}

You'd then call it with:

totals = CalculateTotals(table, 
                         row => row.Field<string>("MyColumn") == "Hello");

Is that what you're after?

Answer 2

If you want to store the lambda expression, you need to declare it like so. This would return true if an integer is less than 3 for example:

Func<int,bool> F = o=>o < 3

Then you can pass it around.