get all elements that does not exist in a c# list

Question

I have a list of numbers:

List<int> lstActive = new List<int>{1,6,7,8,10};

I want to get the numbers that does not exit in the above list and less than 10 e.g.

private List<int> GetInactive(List<int> lstActive, int MaxValue)
{
//To Do
}

Then:

List<int> lstInactive = GetInactive(lstActive, 10)

the result should be: {2,3,4,5,9}

How can I do this ?

Take a look at this post: https://stackoverflow.com/questions/3944803/use-linq-to-get-items-in-one-list-that-are-not-in-another-list — David Tansey, Feb 20 '19 at 23:12
Also, you don't have to pass an array to the `List` constructor. You could built it like so: `List lstActive = new List { 1, 6, 7, 8, 10 };` — Robert Stefanic, Feb 20 '19 at 23:16

score 2 · Accepted Answer · answered Feb 20 '19 at 23:14

2

Enumerable.Range(0, maxValue).Where(n => !lstActive.Contains(n))

If perf is an issue, make a hashset:

var hs = new HashSet<int>(lstActive);
Enumerable.Range(0, maxValue).Where(n => !hs.Contains(n))

answered Feb 20 '19 at 23:14

Sava B.

score 1 · Answer 2 · answered Feb 20 '19 at 23:15

1

Try This:

List<int> lstActive = new List<int>(new int[]{1,6,7,8,10}); 
Enumerable.Range(1, 10).ToList().Except(lstActive).Dump();

answered Feb 20 '19 at 23:15

thank you @ppau2004, I as well didn't understand it. It would be very nice if downvoter explains us :) – Derviş Kayımbaşıoğlu Feb 20 '19 at 23:39

2 Answers2