Piano Roll - Is there a keypress that will transpose "selected notes" up an octave ?

On some DAWs you can select a number of notes in the piano roll and press a key and it will transpose the selected notes up one octave, (or up a semitone etc.) Does Reaper have that facility in the piano roll?

Yes, look into the action list. Assign relevant actions to whatever keys you want.

Check the MIDI editor actions list also (top right corner there). Those actions you're showing work only from main arrange view.

Since you're transposing notes you'll probably find this Mouse Modifier behavior quite helpful: Context: [MIDI note] Mouse gesture: [left drag] Modifier: Shift+Ctrl Behavior: "Move note on one axis only" Here it is pictured in REAPER's Preferences window: Check out all the other Mouse Modifers and Actions for the MIDI Editor. There are a lot of very useful options!

Not sure about PRV, but in notation view you just hit "t" and a box come up. You do have to select a value.

My tip above using j,k works of course in notation view as well, it is same midi editor, only a different view.