Error : Number of elements in 'Timestamps' value must be equal to the number of rows of 'Values' value.

I'm coming across this error when I try to execute my code and I'm getting a little bit confused. The purpose of the code is to take data from a particular field from a channel in Thingspeak, analyze it and post the analyzed data to a particular field in another channel. The error is:

Number of elements in 'Timestamps' value must be equal to the number of rows of 'Values' value.

data = thingSpeakRead(ChannelID,'ReadKey',readAPIKey,'Fields',4,'DateRange',[datetime(2019,7,6,14,00,00),datetime('now')]);

%% Analyze Data %%
% Add code in this section to analyze data and store the result in the
% 'analyzedData' variable.
analyzedData = data;

%% Write Data %%
thingSpeakWrite (ChannelID,analyzedData,'WriteKey',writeAPIKey,'Fields',1,'Timestamps',datetime('now'));

Answer 1

[Mario Chiappelli]

I would assume the issue is that you are reading in (for example) 10 data points that match up with 10 date times. You then are writing the 10 analyzed points to thingspeak but you only have one date time that it matches up with.

If you want to store the date times of the incoming points, try something like this:

[data,timestamps] = thingSpeakRead(ChannelID,'ReadKey',readAPIKey,'Fields',4,'DateRange',[datetime(2019,7,6,14,00,00),datetime('now')]);

To fix the problem I would suggest to change the datetime after the 'TimeStamps' to something that reflects the appropriate timestamps of the thingspeak data. So, I would utilize the timestamp variable created above. Try this,

lastTime = length(timestamps);
thingSpeakWrite (ChannelID,analyzedData,'WriteKey',writeAPIKey,'Fields',1,'timestamps',[timestamp(1),timestamp(lastTime)];

[Smart Grid]

I made the changes, but now it tells me that 'Daterange' is not a recognized parameter in the thingSpeakWrite function

Error using Data aggregation

'DateRange' is not a recognized parameter

[data,timestamps] = thingSpeakRead(681431,'ReadKey',readAPIKey,'Fields',4,'DateRange',[datetime(2019,7,6,14,00,00),datetime('now')]);

%% Analyze Data %%
% Add code in this section to analyze data and store the result in the
% 'analyzedData' variable.
analyzedData = data;
lastTime = length(timestamps);
thingSpeakWrite (706490,analyzedData,'WriteKey',writeAPIKey,'Fields',1,'DateRange',[timestamps(1),timestamps(lastTime)]);

[Walter Roberson]

Are you deliberately changing the timestamps associated with the data you read in? If so then taking into account that the timestamps must be unique, how do you want to retimestamp the data?

Why not just pass 'timestamps', timestamps as the option, writing out the same timestamp as you read in?

[Mario Chiappelli]

Do what Walter said and change the 'DateRange' option to 'timestamps'

That was my bad, before you were sending date time values and now you are sending timestamp values. They are the same concept just different input formats.

I changed my code above.

[Walter Roberson]

[data,timestamps] = thingSpeakRead(681431,'ReadKey',readAPIKey,'Fields',4,'DateRange',[datetime(2019,7,6,14,00,00),datetime('now')]);

%% Analyze Data %%
% Add code in this section to analyze data and store the result in the
% 'analyzedData' variable. This assumes that the number of output rows
% is the same as the number of input rows
analyzedData = data;

thingSpeakWrite (706490,analyzedData,'WriteKey',writeAPIKey,'Fields',1,'Timestamps',timestamps);

If the number of output rows is not the same as the number of input rows, then you need to figure out what meaningful timestamps would be, taking into account that the timestamps must be unique for the channel.