Lambda expressions: index of an element in the array

Question

int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
int oddNumbers = numbers.Count(n => n % 2 == 1);
var firstNumbersLessThan6 = numbers.TakeWhile(n => n < 6);
var firstSmallNumbers = numbers.TakeWhile((n, index) => n >= index);

These are C# code taken from http://msdn.microsoft.com/en-us/library/bb397687.aspx

I understand the first two lambda expressions just fine by considering n as an element of the array "numbers".

However the third lambda expression is really confusing with "index". Is (n,index) one of the lambda parameters well established for arrays? Is this a convention?

index meens index of element in array and this expression returns all the elements in the numbers array until a number is encountered whose value is less than its position.OK ? — Farrokh
– Farrokh, Commented Jul 24, 2014 at 19:21
It's just part of the delegate that TakeWhile() accepts. You can read about it here: msdn.microsoft.com/en-us/library/vstudio/…. Check out the predicate parameter. — itsme86
– itsme86, Commented Jul 24, 2014 at 19:23
What did you find when you looked at the documentation of that particular method, and what aspect of that did you find confusing? — Servy
– Servy, Commented Jul 24, 2014 at 19:53

Lee Grissom · Accepted Answer · 2014-07-24 19:42:53Z

1

When TakeWhile iterates over the collection:

n is the value of the element
index is the index of the element

int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
// As TakeWhile iterates over the array: 
//   "n" is the value of the element
//   "index" is the index of the element
var firstSmallNumbers = numbers.TakeWhile((n, index) => n >= index);
foreach(var n in firstSmallNumbers)
    Console.WriteLine(n);

Output:

5
4

Run this at: https://dotnetfiddle.net/4NXRkg

answered Jul 24, 2014 at 19:42

Lee Grissom

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