Building int[] from values in another int[]

Question

I have an int[] building; that I want to instantiate dynamically based on another array int[] info;

The info will hold int ranging from 0-48

To build the building array.. If there is a non-zero value in the info array at index ind I want to add that index to the building array.

So if info looks like this {0, 12, 24, 48} I'd like building to show {1, 2, 3} another example {12, 0, 0, 48} -> {0, 3}

Is there a neat one liner to accomplish this?

How I have been doing it

int[] info = new int[]{12, 0, 0, 48};
List<int> indxs = new List<int>();
for (int i = 0; i < info.Length; i++)
    if (info [i] > 0)
        indxs.Add(i);
int[] building = indxs.ToArray();

The language you're using is not C++, but the question is tagged C++. Please fix this inconsistency. Adjust either the tag or the example. — Cheers and hth. - Alf
– Cheers and hth. - Alf, Commented May 15, 2014 at 13:15
You might write a helper, say IndexesWhere, similar to System.Linq.Enumerable.Where. — ach
– ach, Commented May 15, 2014 at 13:19
Is there a particular reason you want it to be a one liner? You can create a method in a utility library, or better yet an extension method. You should always value readability over length. — mason
– mason, Commented May 15, 2014 at 13:23
@mason Not specifically, when performance isn't too much of an issue I like to make my code look nice. // I like the idea of extension methods. I can just push all the "mess" to one class and make the rest of my code look nice. — AnotherUser
– AnotherUser, Commented May 15, 2014 at 13:25
One liners do not necessarily make code look nice. Sure, in some cases you can do some very readable one liners with Linq or lambdas. But trying to make it a one liner for the sake of saving space is a bad idea. — mason
– mason, Commented May 15, 2014 at 13:27

Mike Perrenoud · Accepted Answer · 2014-05-15 13:23:37Z

4

var building = info.Select((i, idx) => i == 0 ? -1 : idx)
                   .Where(i => i != -1)
                   .ToArray();

This will get you the same array as you're getting now.

Here is the entire console application I used to prove it:

class Program
{
    static void Main(string[] args)
    {
        int[] info = new int[] { 12, 0, 0, 48 };
        List<int> indxs = new List<int>();
        for (int i = 0; i < info.Length; i++)
            if (info[i] > 0)
                indxs.Add(i);
        int[] building = indxs.ToArray();

        var newBuilding = info.Select((i, idx) => i == 0 ? -1 : idx)
            .Where(i => i != -1)
            .ToArray();
    }
}

Both building and newBuilding provide you with the same output.

answered May 15, 2014 at 13:23

Mike Perrenoud

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Comments

leskovar · Accepted Answer · 2014-05-15 13:24:25Z

2

var filtered = info.Select((x,i) => new { Value = x, Index = i})
                   .Where(x => x.Value > 0)
                   .ToArray();

answered May 15, 2014 at 13:24

leskovar

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