Lambda expressions with List in C#

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Please consider this example,

List<int> lst = new List<int> { 1, 2, 3, 4 };
int result = lst.Aggregate((x, y) => x * y);

As per the articles (x,y) specifies input parameters and x*y as implementation, my doubt is, aggregate() is the method of list, then it has to have inner implementation of aggregation by its own, then what (x*y) specifies or rather needed here...

Please mention the articles explaining lambda and list separately...

Thanks in advance,

Posted 16-Jul-13 21:10pm

Chaitanya Pai

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Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) · Accepted Answer · 2013-07-16T22:46:00

Solution 1

Here x * y indicates that the elements will be aggregated by multiplication.

Refer - C# Aggregate[^].
See the examples and their outputs. You will be clear.

Quote:

C#

int[] array = { 1, 2, 3, 4, 5 };
	int result = array.Aggregate((a, b) => b + a);
	// 1 + 2 = 3
	// 3 + 3 = 6
	// 6 + 4 = 10
	// 10 + 5 = 15
	Console.WriteLine(result);

	result = array.Aggregate((a, b) => b * a);
	// 1 * 2 = 2
	// 2 * 3 = 6
	// 6 * 4 = 24
	// 24 * 5 = 120
	Console.WriteLine(result);

Posted 16-Jul-13 22:46pm

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ)

Comments

Chaitanya Pai 17-Jul-13 4:51am

Thanks for the reply. Why cant i pass (a => a>2), why only (a,b)...

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) 17-Jul-13 5:44am

Aggregate function will work on two elements at a time. That's why. And I guess you are now clear after referring to the answer by OriginalGriff...

OriginalGriff · Accepted Answer · 2013-07-16T22:53:00

A lambda is pretty much just a method without a name. The (x,y) part before the => specifies the parameters and the x * y part after it is the body of the function.
In this case, what you are doing is the equivalent of:

C#

List<int> lst = new List<int> { 1, 2, 3, 4 };
int x = 0;
for (int i = 0; i < lst.Count; i ++)
    {
    int y = lst[i];
    x = i == 0 ? y : x * y;
    }
int result = x;

Only with deferred execution (don't worry about that for the moment).

[edit]Spurious HTML closing tags removed - OriginalGriff[/edit]