Write a table using thingSpeakWrite
Latest activity Reply by Juan Manuel Romero Arguello
on 24 May 2022
I am trying to write a table to a TS channel using thingSpeakWrite. The code below results in error but the help documentation indicates that it can be done. Any suggestion on how to fix this?
Function to call:
thingSpeakWrite(channelID,ship1(1,:),'WriteKey',writeAPIKey);
The complete code:
%Initialize table to be written to ThingSpeak
varNames = ["MMSI", "LAT", "LONG", "SOG", "VesselName", "VesselType", "Length", "Width"];
varTypes = ["double", "double", "double", "double", "categorical", "double", "double", "double"];
ship1 = table('Size',[20 8],'VariableTypes',varTypes,'VariableNames',varNames);
ship1.MMSI(:) = 121212;
ship1.SOG(:) = 10;
ship1(:,5) = {'PRIMODY'};
ship1(:,6) = {37};
ship1.Length(:) = 20;
ship1.Width(:) = 12;
thingSpeakWrite(channelID,ship1(1,:),'WriteKey',writeAPIKey);
6 Comments
Time Descending
You need to specify times.
Adding time stamps won´t solve the issue. The code: thingSpeakWrite(channelID,ships(1,:),'WriteKey',writeAPIKey,'TimeStamp', datetime('now')); results in the error: Data must be a 1-D cell array.
I think it has to do with the fact that the table has mixed data types: double and categorical. Is it possible to write the whole table in that case?
The size of your timestamp array needs to match the long dimension of ships(1,:). Right now, you have only one timestamp.
Every feed entry in ThingSpeak needs a unique timestamp. When you send a table of data, ThingSpeak needs a seperate time for each feed entry. See the documentation for thingSpeakWrite(), especially the entry on writing a matrix of data and a timetable. I prefer timetables in ThingSpeak, since they natively have the time column, but with a table, you can also provide the timestamps seperately, as in the matrix example.
I reccomend you write the data to a tiemtable first, then write to ThingSpeak.
The categorical array may also be a problem, but ThingSpeak usually converts everything to a string first.
I see, you only want to write one entry. Sorry about that. Ill see if I can get it to work.
You seem to be correct that it is the cartegorical type causing a problem.
Here is a workaround.
newTable=ship1(1,:);
newTable.VesselName=string(newTable.VesselName);
thingSpeakWrite(1587643, newTable.Variables, 'timestamp', datetime('now'));
That way you can preserve the categorical type in your original ships table.
Note you changed ship1 to ships in the second comment I think.
This works, thanks! I simply want to add that the syntax newTable.Variables must be used. Otherwise, the error Data must be a 1-D cell array persists. Also that for a single entry write, the time stamp could be ommited.
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