For plots the x value may be omitted, and for splots the x and y values may be omitted. In either case the omitted values are assigned the current coordinate number. Coordinate numbers start at 0 and are incremented for each data point read.
To specify other formats, see plot datafile using.
In the plot command, blank lines in the data file cause a break in the plot. There will be no line drawn between the preceding and following points if the plot style is lines or linespoints (see plot style). This does not change the plot style, as would plotting the data as separate curves.
This example compares the data in the file population.dat to a theoretical curve:
pop(x) = 103*exp((1965-x)/10)
plot [1960:1990] 'population.dat', pop(x)
The file population.dat might contain:
# Gnu population in Antarctica since 1965
1965 103
1970 55
1975 34
1980 24
1985 10
When a data file is plotted, samples and iso_samples are ignored. Curves plotted using the plot command are automatically extended to hold the entire curve. Similarly grid data plotted using the splot command is automatically extended, using the assumption that isolines are separated by blank lines (a line with only a CR/LF in it).
Implicitly, there are two types of 3-d datafiles. If all the isolines are of the same length, the data is assumed to be a grid data, i.e., the data has a grid topology. Cross isolines in the other parametric direction (the ith cross isoline passes thru the ith point of all the provided isolines) will also be drawn for grid data. (Note contouring is available for grid data only.) If all the isolines are not of the same length, no cross isolines will be drawn and contouring that data is impossible.
For splot if 3-d datafile and using format (see splot datafile using) specify only z (height field), a non parametric mode must be specified. If, on the other hand, x, y, and z are all specified, a parametric mode should be selected (see set parametric) since data is defining a parametric surface.
A simple example of plotting a 3-d data file is
set parametric
splot 'glass.dat'
or
set noparametric
splot 'datafile.dat'
where the file datafile.dat might contain:
# The valley of the Gnu.
10
10
10
10
5
10
10
1
10
10
0
10
Note datafile.dat defines a 4 by 3 grid ( 4 rows of 3 points each ). Rows are separated by blank lines.
On some computer systems with a popen function (UNIX), the datafile can be piped through a shell command by starting the file name with a '<'. For example:
pop(x) = 103*exp(x/10)
plot '< awk "{print $1-1965 $2}" population.dat', pop(x)
would plot the same information as the first population example but with years since 1965 as the x axis.
For more information about 3-d plotting, see splot.