Fold

Applies a function to each element of the collection, threading an accumulator argument through the computation. Take the second argument, and apply the function to it and the first element of the collection. Then feed this result into the function along with the second element and so on.

This method is very similar to Reduce, but in this case is considered a initial state.

Parameters	Returns
Func<TState, T, TState> folder TState state IEnumerable<T> source	TState

Usage

Accumulating an individual property of each element through a collection

//IEnumerable<Animal> source = 
//    { ("Cats",4), ("Dogs",5), ("Mice",3), ("Elephants",2) }

int result = source.Fold( 6, (_state, element) => _state + element.Item2);

//result = 20

When the type of elements in your collection are: int, decimal, double, string or bool you can also use this function combined with the Operations described in operations section as folder functions.

Using an operation as a folder

//IEnumerable<int> source = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }
int result = source.Fold(15, IntegerOperations.Add);

//result = 15 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10
//result = 70