How to make gnuplot to NOT plot multiple lines?

Question

I am plotting some data and I am getting multiple lines streaking across the plot. There should be one line, so I imagine that gnuplot is trying to fit the data and is joining points or something in a strange way. How can I get gnuplot to plot one like instead of multiple lines? Here is my script:

set term png font 'Liberation Sans,10' size 800,200
set output "data/values.png"
set style line 1 lt 1 lw 1 lc rgb "purple" pt -1
set xlabel "Time" font 'Liberation Sans,10'
set xdata time
set timefmt "%Y-%m-%d %H:%M:%S"
set xtics font 'Liberation Sans,10'
set ytics font 'Liberation Sans,10'
set autoscale y
plot "data.txt" using 1:5 ls 1 smooth bezier with lines

Output of the gnuplot script

since the line is connected, i'd guess your data isn't sorted by x axis value, so it's going back and forth. if there were disconnects, i'd expect blank lines in the data file. — Jay Kominek
I thought of this, the data is sorted by time ... but I will look at it again, I am pulling it from a database, and it has never been out of order. — Xofo
if you're using a sql server, then unless you specifically tell it you want the data sorted, it can do whatever it wants. and probably will. — Jay Kominek
Plot time against line number to check if your data is continous with "plot datafile using 0:1". If this goes up and down you know where you are with your data. — Karl

Miguel Miguel · Accepted Answer · 2015-06-07T21:22:50

You can use sort to sort your data. Consider the following data file which I have generated consistent with your time format:

2000-12-21 12:32:05 1
2001-11-21 12:32:05 2
2000-12-20 12:32:05 3
2000-12-20 12:32:04 4

Typing sort data.txt will yield the correct ordering:

2000-12-20 12:32:04 4
2000-12-20 12:32:05 3
2000-12-21 12:32:05 1
2001-11-21 12:32:05 2

You can invoke this within gnuplot by using a special input name plot "< sort data.txt" ...:

set xdata time
set timefmt "%Y-%m-%d %H:%M:%S"
plot "data.txt" using 1:3 w l

enter image description here

set xdata time
set timefmt "%Y-%m-%d %H:%M:%S"
plot "< sort data.txt" using 1:3 w l

enter image description here

You can consult the sort documentation if you need more powerful sorting with respect to your data format.

How to make gnuplot to NOT plot multiple lines?

1 Answers