Assuming we have the following IEnumerable example:
IEnumerable<int[]> veryLargeJaggedArray =
{
new int[] {1, 3, 5},
new int[] {0, 2, 4},
new int[] {11,22,6},
...lots of data streaming in
}
where the underlying collection is not based on ICollection (i.e. no fast Count() lookup), what is the most efficient way to apply c# Linq to perform aggregate type column operations?
This question extends my previous question to a more practical case.
You can easily create your own method to generate a sequence representing a column given that input:
public static IEnumerable<T> GetColumn<T>(
this IEnumerable<IList<T>> data,
int columnNumber)
{
return data.Select(row => row[columnNumber]);
}
Now you can write code like:
var firstColumnSum = veryLargeJaggedArray.GetColumn(0).Sum();
var secondColumnAverage = veryLargeJaggedArray.GetColumn(1).Average();
The built-in extension methods are already pretty smart. You typically just need something like this:
var result = MyCollection.Sum();
or
var result = MyCollection.Average(i => i.NumericProperty);
These extension methods take advantage of overloading and polymorphism, such that if your underlying collection type implements IList<T>, that version of the method (which can take advantage of a Count property) will be called, but if only IEnumerable<T> is available, then the IEnumerable<T> will run.
