ThingSpeak: How to set 'NumPoints' equal to the maximum available in the channel?

Question

Luke Martin 2021-11-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1588144-thingspeak-how-to-set-numpoints-equal-to-the-maximum-available-in-the-channel

回答： Rogier 2022-7-13

采纳的回答： Vinod

在 MATLAB Online 中打开

Hi folks,

I'm looking for a way to set the '2733' in my command below equal to the amount of datapoints available.

[data, time] = thingSpeakRead(readChannelID, 'Field', fieldID1, 'NumPoints', 2733, 'ReadKey', readAPIKey);

For context, I'm trying to setup visualisations that still work when the dataset in the channel is changed. For my current dataset, I have 2733 lines so the above works, but I'd like to get it to the point where it can work without amendment when I change the dataset.

Thanks!

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Answer 1

Vinod 2021-11-16

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https://ww2.mathworks.cn/matlabcentral/answers/1588144-thingspeak-how-to-set-numpoints-equal-to-the-maximum-available-in-the-channel#answer_833059

See this documentation. The NumPoints can be at max 8000. If you have less than 8000 points in your channel, everything is returned. If you have >8000 points, only the most recent 8000 are returned.

I'd recommend also answering this survey from the developers as they are looking to provide functionality based on use cases.

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Luke Martin 2021-11-17

Thanks Vinod!

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Answer 2

Rogier 2022-7-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1588144-thingspeak-how-to-set-numpoints-equal-to-the-maximum-available-in-the-channel#answer_1006115

在 MATLAB Online 中打开

I have written this bit of code to help with this problem for myself, figured I'd share

% Channel to read from
readChannelID = 123456789;
% Set these to start & end of the data you're interested in
startDate = datetime('2022-07-06');
endDate = datetime('now');
% How often data is logged, max. This example is once per minute.
% If you don't know exactly, make sure this is higher. So if it
% is roughly once a minute, but can sometimes be twice a minute for
% a bit, be safe and set to '2' and 'minute' for twice a minute.
frequencyTimes = 1;
frequencyPer = 'minute'; % can be 'year', 'month', 'day', 'hour', 'minute', 'second', or 'millisecond'
% Example of output data
total = 0;
% Leave this block alone
rangeEndDateNum = addtodate(datenum(startDate), 8000 / frequencyTimes, frequencyPer);
rangeEndDate = datetime(rangeEndDateNum, 'ConvertFrom', 'datenum');
dateRange = [startDate, rangeEndDate];
diff = rangeEndDate - startDate;
while dateRange(1) < endDate
    if dateRange(2) > endDate
        dateRange(2) = endDate;
    end
    % Retrieve data
    [data, time, info] = thingSpeakRead(readChannelID, DateRange=dateRange);
    % Do something with data
    numberOfElements = numel(time);
    % Accumulate with previous data
    total = total + numberOfElements;
    % This sets up the next chunk
    dateRange = dateRange + diff;
end
% Do something with the accumulated data
display(total, 'Total number of datapoints in ThingSpeak channel')