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I want to add an offset to the data from a file which i want to plot using gnuplot. Suppose i want to add an offset of 0.001 to all the data values from file before i plot them . How can i do it in gnuplot without having to rewrite the data file with the offsets.

Thanks.

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2 Answers 2

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21

Try something like this:

plot "Data.dat" u ($1):($2 + 0.001) w l

The $1 and $2 specify the column you want to plot. Simply add a constant like 0.001 to the column or even add two columns like so: $1 + $2.

I hope that answers your quastion
Cherio Woltan

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2 Comments

To clarify how to add offset to X column when not specifying X column: Note that "$0 or column(0) returns the sequence number of this data record within a dataset." When you are plotting and just specifying the y-coord (e.g. 'plot "datafile" using 2 with lines') then you are implicitly using the column(0). That plot command is the same as 'plot "datafile" using 0:2 with lines'. To add an X-offset and/or Y-offset you can change it like this: 'plot "datafile" using ($0+17):($2+42) with lines'.
I have to say the whole shortcut syntax, especially in examples, makes it ever harder to read - was it really that much effort to write with lines instead of w l and using instead of u? gnuplot should really do away with the whole abbreviated syntax altogether. It does not serve anybody except perhaps spare the script interpreter some CPU time.
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I think it is better to let gnuplot compute offset, instead of guessing the right constant...

off(x) = sin(x) + offset
fit off(x) "data" using 1:2 via offset
plot off(x)
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