Getting common values in two array issue using LINQ

Question

I have two arrays say

var list1 = string[] {"1", "2", "3", "4", "", ""};
var list2 = string[] {"2", "3", "4","",""};

When i try to get common items form these two array using following code

 var listCommon = list1.Intersect(list2);

It gives me result like this

string[] {"2", "3", "4", ""}

But i want it should return like this

string[] {"2", "3", "4", "", ""}

It is escaping last empty string value while intersecting.

@DavidArno Actually that question is a little different. That question would expect to get {"2", "2", "3", "3, "4", "4", "", "", "", ""} for the example given here. — juharr
– juharr, Commented Oct 11, 2013 at 11:55

Tim Schmelter · Accepted Answer · 2013-10-11 11:45:22Z

9

Set methods like Intersect or Except remove duplicates from each collection. I assume you want something like this instead:

var listCommon = list1.Where(list2.Contains);

which is not as efficient. This could be an optimization:

var l2Lookup = new HashSet<string>(list2);
var listCommon = list1.Where(l2Lookup.Contains);

edited Oct 11, 2013 at 11:45

answered Oct 11, 2013 at 11:39

Tim Schmelter

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3 Comments

David Arno Over a year ago

Interesting. I notice you are less keen to close/delete questions when you are raking in the rep from it, Tim...

Tim Schmelter Over a year ago

@DavidArno: I have no idea what you're talking about. I have not noticed the duplicate vote until now. But even if, do i get a downvote from you because i answer a question that you have voted to close ?

juharr Over a year ago

Of course if the second list only contains one empty string this would still return two empty strings, because the first list has two. Not sure if that's exactly what the OP wants, but the other way would definitely be more complex.

Anarion · Accepted Answer · 2013-10-11 11:41:19Z

7

This will work:

list1.Where(x=>list2.Contains(x))

answered Oct 11, 2013 at 11:41

Anarion

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3 Comments

Anarion Over a year ago

Too bad, i'm too late )

Andrey Rybalkin Over a year ago

But your answer is better :) I cant understood what meens "list1.Where(l2Lookup.Contains)" in top answer. But your answer made it clear. Thank you @Anarion

Anarion Over a year ago

@Andrey Rybalkin Keep in mind that Solution in answer by Tim Schmelter is way more efficient, because it's much faster to search in HashSet.

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