When I prefix the J ("join") command with a count, Vim is joining one fewer line than I expect. For example, with the cursor at the first column, first line of the following,
one
two
three
four
five
if I type JJJJ (four J's), I get (as expected):
one two three four five
But if instead I type 4J, I get:
one two three four
five
It looks like J=1J=2J, 3J=JJ, 4J=JJJ, and so on. Is this the expected behavior?
After further research and office discussion, I realize this is indeed the expected behavior. According to the vim help:
J Join [count] lines, with a minimum of two lines.
I've always thought [count][command] was literally another way to type [command] repeated [count] times. Turns out commands are free to interpret [count] as they like, and J takes it to mean the number of lines that will be joined; this explains why 1J and 2J have the same effect.
It is the described behaviour.
:help J states
Join [count] lines, with a minimum of two lines
