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Enumerable Skip

I have two codes as follow,

Code 1
           int[] grades = { 1, 2, 3, 4, 5 };

            var q = from c in grades.Skip(1)
                    select c;

            foreach (int number in q)
                Console.WriteLine("{0}", number);

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Code 2
            int[] grades = { 1, 2, 3, 4, 5 };

            var q = from c in grades
                    where c > 1
                    select c;

            foreach (int number in q)
                Console.WriteLine("{0}", number);

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They provide the same result.
If the list contains billion values and filter condition is different, base on the performance which one is better?
0
mawingpui
Asked:
mawingpui
3 Solutions
 
kris_perCommented:

Code 1 which uses Skip would be faster as Code 2's 'where c > 1' is checked on every item.
0
 
Gururaj BadamCommented:
I don't think there will be any performance difference between the two.

The third way would be - var q = grades.Where(x => x > 1);

a more simpler notation though.

I can only recommend you to test to see the execution time required in all 3 approaches and decide which one is better suitable for you.
0
 
CyberSoftCommented:
There are actually two fundamental differences in the logic of the two code-snippets above.

Code 1: Ignores the first record in the result set (regardless of value)

Code 2:: Excludes values from the result set where the grade is less than or equal to 1

If there is ordering involved or other records with the same values as in the where clause you'll get two distinctly different result sets which means you may not necessarily get the same results from both queries.

HTH
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