在Linq中传递参数

Question

I have the following code within a method:

someData = table.AsEnumerable()
    .Where(row => row.someRow.Equals("Something"))
    .Sum(row => row.AnotherRow);

On the last line I want to pass in a parameter from somewhere else which will replace .AnotherRow

In other words, something like:

.Sum(row => row. + myParameter);

Any ideas? I get an error when I try the above. Would appreciate any help.

Answer 1

You cannot pass something that would represent .AnotherRow , but you can pass a functor that picks the desired attribute from your object.

Let's say table is IEnumerable<MyClass> . Then you can do this:

int SumSelected(Func<MyClass,int> attrSelector) {
    return table.AsEnumerable()
        .Where(row => row.someRow.Equals("Something"))
        .Sum(row => attrSelector(AnotherRow));
}

Now you can call this method with a "selector" that designates the attributes to be added up, as follows:

var totalCustomers = SumSelected(obj => obj.CustomerCount);
var totalStores = SumSelected(obj => obj.StoreCount);

Answer 2

I think:

someData = table.AsEnumerable()
    .Where(row => row.someRow.Equals("Something"))
g.Sum(row => Calculate(row => row.AnotherRow, row1 =>row1.AnotherRow));

Method Calculate:

 private double Calculate(double d1, double d2)
    {
        return d1 + d2;
    }