Are there any episodes where one of the main characters are missing for almost the entire epsiode

I was just watching "The One with the Mugging" and realised Rachel says only like one line or two and just doesn't appear for the rest of the episode. She wasn't included in any of the storylines. The storylines in that episode are Ross finding out Phoebe mugged him, Monica helping Chandler with the fire sneakers and Joey with the "Holding in his piss" acting. The only scene Rachel was in is Chandler asking her if the shoes are a good idea for Ralph Lauren or something.

I'm just wondering if there are anymore. I've noticed some episode where Monica is behind the scenes a lot more in the later seasons.