Can't get Perl Chart (gnuplot) to label all tics on axis - perl

Question

Using Chart::Gnuplot in perl.
The x axis is to be for date/time.
I'm specifying
timeaxis => "x" (seems to work)
I'm using
timefmt => '%Y-%m-%d_%H:%M:%S'
to read the elements in the array ref passed to xdata in the Chart::Gnuplot::DataSet->new. (that seems to work too)
Using
xtics => {labelfmt => "%m-%d %H", rotate => -90}
to display the labels the way I want them. (that all seems to work too)
And indeed, everything looks good except for the fact that it's only labeling a handful of tics on the x (date/time) axis. I want to label them all (or every other one, or have some control over this)
I found lots of examples of how to do this for numbers (note dates) using... start, incr, end, etc... . And I tried lots of experiments to get this to work. But I think I've exhausted all that I can find on this googling around and I'm still stuck :-(
And so, if there is any advise on how to get this to label all the tics with the date/time, I'd very much appreciate it.

Answer 1

You can use xtics => { labels=>[...] } but you need to respect that
In case of timeseries data, position values must be given as quoted dates or times according to the format timefmt.
from gnuplot documentation.
Assuming the array #x contains the data set's time values in timefmt, x-tick labels can be forced at each of those times like this.
xtics => {
labels=>[map { q(').$_.q(') } #x]
}
There are plenty of ways to add single quotes around each time, but I think the map above is cleanest.
You can of course provide your own labels, just make sure they are quoted properly and the same as timefmt. I think Perl's q() quoting operator is the way to go.
labels=>[ q('2005-6-7_07:04:53') , q('2005-6-7_07:05:10') ]
Full working example
Here is a full working example, modified from the gnuplot tick examples.
#!/usr/bin/perl -w
use strict;
use Chart::Gnuplot;
# Change the date time format of the tic labels
# - the solution is the same as change the number format
# Date array
my #x = qw(
2005-6-7_07:00:00
2005-6-7_07:05:00
2005-6-7_07:10:00
2005-6-7_07:15:00
);
my #y = qw(
3562279127
3710215571
3877469703
3876354871
);
# Create the chart object
my $chart = Chart::Gnuplot->new(
output => 'test.png',
xtics => {
rotate => -90,
labelfmt => "%m-%d %H",
labels=>[map { q(').$_.q(') } #x]
},
timeaxis => "x", # declare that x-axis uses time format
);
# Data set object
my $data = Chart::Gnuplot::DataSet->new(
xdata => \#x,
ydata => \#y,
style => 'linespoints',
timefmt => '%Y-%m-%d_%H:%M:%S',
);
# Plot the graph
$chart->plot2d($data);
Without the labels, you'll get something like this.
With the labels, you'll get something like this.