Your Java is showing :-)

Since he capitalized the method names, it's more likely C#.

The c# user just writes arr.Select(el => el == condition);

Yes, but this function is defined as in-place replacement.

So arr = arr.Select(el => el == condition);

I'd push-back in code-review anyone who tried to do something not in obvious, idiomatic (read: LINQ) C#.

Showing my own ignorance. My heuristics have been updated -- thanks!

It could be Algol or any of its derivatives. :)

Good eye.