I've never had to do this before so I'm at a bit of a loss, but it seems there should be a way...?
 
Let's say I have many MIDI notes that are split in various places but are butting up right against each other. Is there a way to select a bunch of clips and join all adjacent MIDI notes in one go? I can do this manually one note at a time but that would be very time consuming since there are many.
 
Before:
|---------||--------|     |-----------|
 
After:
|-------------------|     |-----------|

What is your definition of "adjacent"?
 
The time between the end of a note and the start of the next one?
The time between the start of a note and the start of the next one?
 
Measured in ticks (per quarter note)?
 
I assume you mean the same pitch. 
 
 

I don't know if a way exists today but it could be scripted. UNDUPE.CAL would get you most of the way there.

Jackson,
 
Yes same pitch. The next note starts on or within a few ticks of the previous note's end. As if you previously split the note, but now want to join them back again.
 
 
Scook,
 
I was looking through the CAL scripts but didn't find an exact match. So yea I could try your suggestion and modify the UNDUP.CAL one. Been a while since I worked with CAL scripts...

You can join MIDI notes easily in the step sequencer. Convert the clip to a step-sequenced one (you can do this quantized or retain offsets, check the documentation). Ctrl-drag across the notes you want to join, then bounce the step-sequenced clip to itself. If you open this clip in the piano roll view, the notes will be joined.

Anderton
You can join MIDI notes easily in the step sequencer. Convert the clip to a step-sequenced one (you can do this quantized or retain offsets, check the documentation). Ctrl-drag across the notes you want to join, then bounce the step-sequenced clip to itself. If you open this clip in the piano roll view, the notes will be joined.

Craig, thanks excellent tip! I'll try it.

I know it's a workaround, but I often switch between step sequencer and piano roll view for various reasons. I had always thought the step sequencer was, well, a "step sequencer" - but it's a powerful, alternate way to work with MIDI data once you find out its particular talents.

Why not just delete the second note, then extend the first one to the same end point? 

Another method is in the piano roll view click on the draw icon in the smart tool window, put the cursor near the end of the first note, hold down the left mouse button and drag the cursor over the notes that you want to connect.

MondoArt
Why not just delete the second note, then extend the first one to the same end point? 

 
Because there are A lot of them and it would be very time consuming as stated earlier.
 

MarioD
Another method is in the piano roll view click on the draw icon in the smart tool window, put the cursor near the end of the first note, hold down the left mouse button and drag the cursor over the notes that you want to connect.

This might be a bit easier but still time consuming. Thanks for the tip, I didn't know about that one.