micahhoover - 2 months ago 34

C# Question

I am trying to find a way to access previous values from a Linq method in the same line.

I want to be able to use this general form in Linq:

`var values = Enumerable.Range( 1, 100 ).Select( i => i + [last result] );`

But I can't find a way to do something like this without multi-line lambda's and storing the results somewhere else.

So the best fibonacci sum I've been able to do in Linq is:

`List<int> calculated = new List<int>( new int[] { 1, 2 });`

var fibonacci = Enumerable.Range(2, 10).Select(i =>

{

int result = calculated[i - 2] + calculated[i - 1];

calculated.Add(result);

return result; // and how could I just put the result in fibonacci?

}

);

Which seems ugly. I could do this in less code with a regular for loop.

`for (int i = 2; i < 10; i++)`

{

calculated.Add(calculated[i - 2] + calculated[i - 1]);

}

It seems like if I could find a way to do this, I could use Linq to do a lot of Linear programming and sum a lot of iterative formulas.

Answer

If you are looking for a way to create a Fibonacci sequence generator, you would be better off writing your own generator function instead of using Linq extension methods. Something like this:

```
public static IEnumerable<int> Fibonacci()
{
int a = 1;
int b = 0;
int last;
for (;;) {
yield return a;
last = a;
a += b;
b = last;
}
}
```

Then you can apply Linq methods to this enumerable to achieve the result you want (try iterating over `Fibonacci().Take(20)`

for example).

Linq extension methods are not the solution for every programming problem, and I can only imagine how horrid a pure LINQ Fibonacci sequence generator would look.