Linq: Exclude results using Zip

Question

I have a list of bool, and a list of strings. I want to use IEnumerable.Zip to combine the lists, so if the value at each index of the first list is true, the result contains the corresponding item from the second list. In other words: ``` List listA = {true, false, true, false}; List listB = {"alpha", "beta", "gamma", "delta"}; IEnumerable result = listA.Zip(listB, [something]); //result contains "alpha", "gamma" ``` The simplest solution I could come up with is: ``` listA.Zip(listB, (a, b) => a ? b : null).Where(a => a != null); ``` ...but I suspect there's a simpler way to do this. Is there?

Accepted Answer

I think this is simpler:

```
listA
 .Zip(listB, (a, b) => new { a, b } )
 .Where(pair => pair.a)
 .Select(pair => pair.b);
```

That logically separates the steps. First, combine the lists. Next, filter. No funky conditionals, just read it top to bottom and immediately get it.

You can even name it properly:

```
listA
 .Zip(listB, (shouldIncludeValue, value) => new { shouldIncludeValue, value } )
 .Where(pair => pair.shouldIncludeValue)
 .Select(pair => pair.value);
```

I love self-documenting, obvious code.

Linq: Exclude results using Zip

Solution

Problem