4 Day temperature comparison, including current day

Question

Mark Clark 2019-2-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/443294-4-day-temperature-comparison-including-current-day

编辑： Yair Altman 2019-2-6

采纳的回答： Omer Yasin Birey

How can I include the current day in the 3 day temperature comparison.

[datetime('today')-days(0),datetime('today')], gives an error

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Mark Clark 2019-2-5

在 MATLAB Online 中打开

% Read temperature data from a ThingSpeak channel for three seperate days 
% and visualize the data in a single plot using the MATLAB thingSpeakPlot 
% function. 
% Channel 12397 contains data from the MathWorks Weather Station, located 
% in Natick, Massachusetts. The data is collected once every minute. 
% Field 4 contains temperature data. 
% Channel ID to read data from 
readChannelID = 569794; 
% Temperature Field ID 
TemperatureFieldID = 1; 
% Channel Read API Key 
% If your channel is private, then enter the read API 
% Key between the '' below: 
readAPIKey = 'MXACLRJMFM18OYOR'; 
temperatureDay0 = thingSpeakRead(readChannelID,'Fields',[TemperatureFieldID], ...
      'NumPoints',240, 'ReadKey',readAPIKey); 
% Read Temperature Data. Learn more about the THINGSPEAKREAD function by 
% going to the Documentation tab on the right side pane of this page.
temperatureDay0 = temperatureDay0(:, 1);
temperatureDay1 = thingSpeakRead(readChannelID,'Fields',TemperatureFieldID, ...
                                              'dateRange', [datetime('today')-days(1),datetime('today')], ...
                                              'ReadKey',readAPIKey); 
temperatureDay2 = thingSpeakRead(readChannelID,'Fields',TemperatureFieldID, ...
                                               'dateRange', [datetime('today')-days(2),datetime('today')-days(1)],...
                                               'ReadKey',readAPIKey); 
temperatureDay3 = thingSpeakRead(readChannelID,'Fields',TemperatureFieldID, ...
                                               'dateRange', [datetime('today')-days(3),datetime('today')-days(2)], ...
                                               'ReadKey',readAPIKey); 
% Create the array of temperatures 
allData=[temperatureDay0(1:240),temperatureDay1(1:240),temperatureDay2(1:240),... 
         temperatureDay3(1:240)]; 
% Learn more about the THINGSPEAKPLOT function by going to the Documentation tab on
% the right side pane of this page. 
thingSpeakPlot((1:240),allData,'legend',{'Day0','Day1','Day2','Day3'}, ...
                        'XLabel','Hour','YLabel','Temperature C', ...
                        'Title','3-Day Temperature Comparison');

Mark Clark 2019-2-5

'DateRange' value must have an end date and time later than the start date and time.

Error message when I use [datetime('today')-days(0),datetime('today')]

Guillaume 2019-2-5

Is that the full text of the error message. Usually it also states which line(s) is responsible for the error. This is essential information we need, particularly since I cannot see anywhere in your code where you use [datetime('today')-days(0),datetime('today')].

On the other hand the error message is clear. The two dates you pass must be different, with the second one later than the first. Of course, subtracting 0 days from a date doesn't change that data, so [datetime('today')-days(0),datetime('today')] is twice the same date.

It's unclear what you expected to do with that.

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Answer 1

Omer Yasin Birey 2019-2-5

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/443294-4-day-temperature-comparison-including-current-day#answer_359615

编辑：Omer Yasin Birey 2019-2-5

在 MATLAB Online 中打开

You can try to use the last minute of the current day, since it says starting date must be before than ending date

todayDate = datetime('today');
todayDate = todayDate + minutes(1439);
[datetime('today')-days(0),todayDate]

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Guillaume 2019-2-6

Well ok, it does create a datetime with a different display format. If that's the whole purpose of subtracting 0, then I would say it's a bad idea. First, you're relying on undocumented behaviour, so that may change in a future release without notice. Secondly, if you want a specific format you'd be better be explicit about the format you want. So even though, 'Format', 'dd, MMM, yyyy HH:mm:ss' might be longer, it's at least very clear what the intent of the code is. Subtracting 0 just to alter the format, with no comment explaining what the purpose is, is just asking for a bug to be introduced later on when a different maintainer notice that 0 subtraction and remove it.

In this particular case, where the array is just passed to another function, the format does not matter at all.

Yair Altman 2019-2-6