Same here!

do you need the join? wouldn't the operand array have the same length?

NM. I see where my logic fails. You get an array of empty strings, so length is NOT the same.

it's readable if you understand regexp.

You're not dumb. It's just another notation that a lot of languages have incorporated. Super useful, but if you haven't invested the time to learn it, you could hardly be expected to know it any more than you could be expected to know Ancient Greek, if you'd never studied it.

It's not that hard to read, if you're familiar with regular expressions. I recommend getting familiar, they are pretty useful.

I had a similar circuit-break approach that avoids processing the whole array if the outlier is close to the beginning, but yours is much more concise. I think readability suffers a bit, but still, nice work.