[Gnuplot-info] Plot command with '-' and '' using same data

[Theo <th...@gm...>]

Hi there,

if I want to include (for some special reason) data into the plotting 
file itself I can use the special filename '-' and write the data in the 
plot file, e.g.:

plot '-' u 0:1 w l lc 1
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20
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e

If I want to use the data twice and modify it in the second plot I 
thought that I can use the special filename '', which according to the 
manual should "...re-use the previous input file in the same plot command."
The previous input file is '-'. As I understand this data should be re-used.

Factor=1.234
Offset=9.876
plot '-' u 0:1 w l lc 1, '' u 0:($1*Factor+Offset) w l lc 2
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20
30
40
e

But it doesn't.
I get the message "warning: Skipping data file with no valid points"
Obviously, I have to type in the same data twice:

Factor=1.234
Offset=9.876
plot '-' u 0:1 w l lc 1, '' u 0:($1*Factor+Offset) w l lc 2
10
20
30
40
e
10
20
30
40
e

Why can't I use the same data twice? Can anybody explain?
Is there a way that I have to type in the data only once?