Expecting support for multiple keys and multiple files.

[Liu G. <goo...@gm...>]

I expect that gnuplot can support multiple keys and multiple files:

<1>.  Multiple keys

I expect that the keys (legends) can be manipulated in groups in stead 
of as a whole objects.

e.g.

set key 1 top right
set key 2 bottom left
plot 'data' t 't1a' key 1, '' t 't1b' key 1, '' t 't2a' key 2, '' t 
't2b' key 2

Thus, if I have many legends and there's no space to put them together, 
I can divide them into two groups
"key 1" and "key 2" and put them at different places.


<2>. Multiple files

Columns from different files can be calculated together. e.g. I have two 
files that have the same format, say, 100 row of (x, y) data, named 
'file1' and 'file2'. Now I want to plot the different between y columns 
from the two files.

plot 'file1' u 1:($2-column('file2',2)) w lp