Octave: Plotyy log files from geothermal heat pump (import/plot datetime) - csv

Question

I'm trying to plot values from my geothermal heat pump log files to analyse it's performance. I tried with excel but it was to slow and not possible to get the plot type I wanted so I'm trying Octave instead. I have absolutely no experience with octave so please forgive my incompetence!
I've processed the .log files with open office calc to get into a decent delimited format. The first column is datetime with the format MM/DD/YY HH:MM:SS, in total there is 21 columns (but I only need 5) and one header line with a label, coma delimiter is '.' and delimiter is ','. The file can be downloaded here and the first 7 columns look like this:
02/19/2018 23:07:00,-0.7,47.5,42,47.3,52.1,1.5
I'm currently trying to plot this with demonstration 3 plotyy from here. Column 2, 3, 5 and 8 imports correctly so I'm figuring it's a problem with the datetime column 1. How can I get Octave to import column 1 correctly and use it as x axis in this plot?:
data=csvread('heatpump.csv');
clf;
hold on
t=data(:,1);
x=data(:,3);
y=data(:,5);
z=data(:,2);
o=data(:,8);
[hax, h1, h2] = plotyy (t, x, t, y);
[~, h3, h4] = plotyy (t, z, t, o);
set ([h3, h4], "linestyle", "--");
xlabel (hax(1), "Time");
title (hax(2), 'Heat pump analysis');
ylabel (hax(1), "Radiator and hot water temp");
ylabel (hax(2), "Outdoor temp and brine out");

Answer 1

There are many, many ways. Here I show you how to read the csv using csv2cell from the io package. I've tried to modify your existing code as less as sane. The first columns is used verbatim (well, I inserted a linebreak) to the plot. There is also a commented version which actually does the conversion and you could then use datetick. Btw, If you add google drive links it would be cool if you add direct links so someone can easily grab the csv or insert the url in the code as I've done, see below.
set (0, "defaultlinelinewidth", 2);
url = "https://drive.google.com/uc?export=download&id=1K_czefz-Wz4HPdvc7YqIqIupPwMi8a7r";
fn = "heatpump.csv";
if (! exist (fn, "file"))
urlwrite (url, fn);
endif
pkg load io
d = csv2cell (fn);
# convert to serial date
# (but you don't have if you want to keep the old format)
#t = datenum (d(2:end,1), "mm/dd/yyyy HH:MM:SS");
data = cell2mat (d(2:end,2:end));
clf;
hold on
t = 1:rows (data);
# Attention: the date/time column time was removed above, so the indizes are shifted
x = data(:,2);
y = data(:,4);
z = data(:,1);
o = data(:,7);
[hax, h1, h2] = plotyy (t, x, t, y);
[hax2, h3, h4] = plotyy (t, z, t, o);
grid on
#set ([h3, h4], "linestyle", "--");
xlabel (hax(1), "Time");
title (hax(2), 'Heat pump analysis');
ylabel (hax(1), "Radiator and hot water temp");
ylabel (hax(2), "Outdoor temp and brine out");
# use date as xtick
# extract them
date_time = d (get(hax2(1), "xtick"), 1);
# break them after the date part
date_time = strrep (date_time, " ", "\n");
# feed them back
set (hax, "xticklabel", date_time)
set (hax2, "xticklabel", date_time)
print ("-S1200,1000", "-F:10", "out.png")