How plot graph with missing data lines? - gnuplot

Question

I have data recorded in time. But some data lines are missing and gnuplot replace them with long lines in these intervals.
How can i set gnuplot to draw nothing instead of draw lines in these intervals?
PS. I don't have free cells in these lines, I dont have these lines at all.
lines:
column 1 ... col 195
13:30:20.8 0.78061899
13:30:21.8 5.969546498
13:32:19.8 17.21257881
13:32:20.8 6.922475345

Answer 1

If you don't want to draw a line between two points you must insert an empty line in the data file between the two point entries, so that effectively you have
13:30:20.8 0.78061899
13:30:21.8 5.969546498
13:32:19.8 17.21257881
13:32:20.8 6.922475345
This cannot be done with gnuplot directly, but you can use e.g. awk to do the processing on-the-fly:
set timefmt '%H:%M:%S'
set xdata time
filename = 'data.txt'
plot 'awk ''{split($1,d,":"); t_prev = t; t = (d[1] * 60 + d[2])*60 + d[3]; if (t_prev && (t - t_prev > 10)) print ""; print }'' '.filename with lines
Here, the gap threshold is 10 seconds.

Answer 2

I suppose your miss data identifier is "NaN", then you can use the following command
plot "data" using 1:($2) with linespoints
instead of
plot "data" using 1:2 with linespoints
The former one will ignore the missing data and treat it as blank line and therefore not draw a connecting line across the gap while the latter one will draw continuous, unbroken line.

Answer 3

Just for the records: there are later questions about the same/similar issue.
Avoid connection of points when there is empty data
How to remove line between "jumping" values, in gnuplot?
Removing vertical lines due to sudden jumps in gnuplot
However, my solutions there require transparent color, which was not available in at the time of OP's question (gnuplot 4.6.5, Feb 2014). Nevertheless, there is a solution without external tools like awk or changing the data.
First solution for gnuplot 4.6.: Instead of a transparent line you use a white line which, however, will cover the grid lines, although it will be hardly visible.
Second solution for gnuplot 4.6 is using vectors. This really interrupts the line and will work for gnuplot 5.x as well.
Data:
00:00:00 0.406406
00:00:44 0.339779
00:01:28 0.986602
00:02:13 0.17746
00:02:57 0.0580277
00:03:42 0.586614
00:04:26 0.84247
00:05:11 0.597502
00:05:55 0.0394846
00:06:40 0.369416
00:13:20 0.527109
00:13:42 0.371411
00:14:04 0.851465
00:14:26 0.980312
00:14:48 0.431391
00:15:11 0.545491
00:15:33 0.708445
00:15:55 0.861669
00:16:17 0.277122
00:16:40 0.787273
Script:
### avoid showing a line across larger time gaps
reset
FILE = "SO26510245.dat"
myFmt = "%H:%M:%S"
tGap = 60 # 60 seconds
set format x "%H:%M"
set timefmt "%H:%M:%S"
set xdata time
set ytics 0.5
set key top center noautotitle
set grid x,y
set multiplot layout 3,1
plot FILE u 1:2 w l lc rgb "red" ti "data as is"
myColor(col) = (t0=t1, t1=timecolumn(1), t1-t0>tGap ? 0xffffff : 0x0000ff)
plot t1=NaN FILE u 1:2:(myColor(1)) w l lc rgb var ti "white line"
myGap(col) = (t1-t0>tGap ? NaN : y0)
plot t1=y1=NaN FILE u (t0=t1,t1=timecolumn(1),t0):(y0=y1,y1=$2,myGap(0)):(t1-t0):(y1-y0) \
w vec lc rgb "web-green" nohead ti "with vectors"
unset multiplot
### end of script
Result: (created with gnuplot 4.6.0, from March 2012)