Plot shows no line, only markers

Hello,

I want to plot two values from a thingspeak channel in a graph.

If I don't use any optional value for LineSpec, I can't see anything plotted although I don't get an error message and the values on x and y axis are in the correct range.

I f I ad for example a 'b.' (for blue points as markers) as LineSpec, I will see the markers but no line. If I ad an '-' for the solid line ('b.-' or 'b-') it doesn't show anything.

This seems very strange to me. I just want a solid line. How can I fix this? Many thanks!

This is my code:

readChannelID = [1....4];
fieldID1 = [1];
fieldID2 = [2];

readAPIKey = 'OA9........MQ';
[data1, time1] = thingSpeakRead(readChannelID, 'Field', fieldID1, 'NumPoints', 600, 'ReadKey', readAPIKey);
[data2, time2] = thingSpeakRead(readChannelID, 'Field', fieldID2, 'NumPoints', 600, 'ReadKey', readAPIKey);
yyaxis left;
plot(time1, data1,'r.')
% nothing is plotted if I use just use  plot(time1, data1)  or if I use  plot(time1, data1,'r-')
yyaxis right;
plot(time2, data2, 'b.');

Answer 1

[Steven Lord]

Do your time and/or data vectors contain NaN values?

any(isnan(time1))
any(isnan(time2))
any(isnan(data1))
any(isnan(data2))

Plotting data containing NaN values leaves a gap in the line where the NaN occurs.

x = 1:10;
y = 1:10;
x(3) = NaN;
y(7) = NaN;
plot(x, y)

With this example there will be a gap between 2 and 4 and between 6 and 8.

[Phillip Maus]

yes, I got it now.

There were missing values, I guess.

Fixed it using the fillmissing - function:

data1 = thingSpeakRead(1....9, 'NumDays', 1, 'ReadKey', 'O.............Q','OutputFormat','timetable');
cleanData1 = fillmissing(data1, 'previous');

yyaxis left;
plot(cleanData1.Timestamps, cleanData1.temp, 'b-');

yyaxis right;
plot(cleanData1.Timestamps, cleanData1.hum, 'r-');

[Walter Roberson]

Gaps are also left at infinite values.