If, at a command prompt, I run
vimdiff file1 file2
I get a vim instance that has two files open side-by-side. Let's suppose that the text in the files looks like this (file1 is on the left, file2 on the right):
╔═══════╤═══════╗
║foo │-------║
║bar │bar ║
║grue │-------║
║~ │~ ║
║~ │~ ║
╚═══════╧═══════╝
Now suppose that my cursor is on the "f" of "foo" and that I wish to copy the first line of file1 to the first line of file2.
One way to do this is to select and yank (copy) the line with v$ y, and then use Ctrl+w l to move the cursor across to the first line of file2, and then type p to paste the copied line. If I do this and I then decide I didn't really want to do it after all, I can press u to undo the paste command I carried out in file2.
Another way to do it is to use the diff put command dp. However, if after doing this I decide I didn't mean to do it, I can't undo it simply by pressing u because my cursor is still in file1 and the u command will undo the most recent change to file1, not the most recent change to file2. So instead I have to use Ctrl+w l or Ctrl+w w to move the cursor to the window for file2 and then press u.
So, my question is: after I have used dp as above, is there any easy way for me to undo it without having to move my cursor across to the other file's window?
There is really no command for this but you could map your own. Put the following in your vimrc and then use du to do diff undos.
nmap du :wincmd w<cr>:normal u<cr>:wincmd w<cr>