Filter array of string with select and a bool array

Question

I need to get all element of a string array where the index in another array of bool is true. In c#, i was looking Select but i don't know how to use on index

String[] ContentArray = {"Id","Name","Username"};
bool[] SelectionArray = {false,true,false};

I have edited your title. Please see, "Should questions include “tags” in their titles?", where the consensus is "no, they should not". — John Saunders
– John Saunders, Commented Nov 14, 2014 at 15:58

Andrew Whitaker · Accepted Answer · 2014-11-14 16:09:14Z

4

I think you're looking for:

IEnumerable<string> strings =
    ContentArray.Where((str, index) => SelectionArray[index]);

Which for your example will yield an IEnumerable<string> containing "Name".

However, if your SelectionArray is shorter than your ContentArray, you will get an index out of bounds exception.

If that's possible, you could simply add a length check, assuming you want an index greater than the length of SelectionArray to return false:

IEnumerable<string> strings =
    ContentArray.Where(
        (str, index) => index < SelectionArray.Length && SelectionArray[index]);

edited Nov 14, 2014 at 16:09

answered Nov 14, 2014 at 15:57

Andrew Whitaker

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1 Comment

juharr Over a year ago

There's an override of Where that gives you the index.

code4life · Accepted Answer · 2014-11-14 16:00:23Z

1

You could also use IEnumerable.Zip(). Here's a sample:

class Program
{
    static void Main(string[] args)
    {
        String[] ContentArray = { "Id", "Name", "Username" };
        bool[] SelectionArray = { false, true, false };

        var selected = ContentArray.Zip(SelectionArray, (s, b) => 
          new Tuple<string, bool>(s, b))
            .Where(tuple => tuple.Item2)
            .Select(tuple => tuple.Item1)
            .ToList();

        foreach (var s in selected)
        {
            Console.WriteLine(s);
        }

        Console.ReadLine();
    }
}

answered Nov 14, 2014 at 16:00

code4life

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2 Comments

D Stanley Over a year ago

+1 for Zip, although you could use an anonymous type instead of a tuple

code4life Over a year ago

Yeah - but I think the sample illustrates the point. So many ways to skin this cat... :)

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