Plot shows no line, only markers

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Phillip Maus
Phillip Maus 2020-9-14
评论： Walter Roberson 2020-9-14
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.');

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回答（1 个）

Steven Lord
Steven Lord 2020-9-14
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.
  2 个评论
Phillip Maus
Phillip Maus 2020-9-14
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
Walter Roberson 2020-9-14
Gaps are also left at infinite values.

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