Monya saw an episode of "This Old House" where they described a new type of plumbing connection. It's called "SharkBite" and it works sort of like the Chinese finger trap toy. You simply slide a pipe into the fitting and it holds. No clamps, no solder, no sweat! It works with copper, or Pex, or even PVC (not that I recommend PVC). Best of all, if you make a mistake, there's a little plastic ring you can use to disconnect it, so you can reconnect it again later. No parts are consumed in the disconnect/reconnect.

It took me a whole day to remove the iron, PVC, and Pex combination shown in the first photo. Most of that time was extracting the iron pipe from the wall. Then it took four hours of measuring and fitting to assemble the copper/SharkBite combination in the wall, and about 30 minutes to measure, cut, and assemble the Pex/SharkBite combination shown in the second photo.

SharkBite fittings are a little expensive, but they don't leak, and they snap together with a click, saving a ton of time. This assembly job would have taken me three days and a call for help from a sweat-joint expert (Dad) if I did it the old way.
The ony drawback is that SharkBite fittings do not hold the pipe rigid. So our bathtub and shower fixtures wobble. I left the wall open on the back side so I can still do something about that if I can think of how.