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Sum query with non-periodic data
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August 25, 2015 - 9:49 am
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I'm posting energy measurements to a channel feed that are not periodic, I mean, one hour there may be 10 values, but the next one there may be 50 or 100. The problem comes when I want to calculate daily totals, because something like this:

returns meaningless values. The reason is that sum simply adds all the values inside each day, and so days with a lot of measurements have higher values than days with fewer.

Is there's some way to calculate a sum taking into account the "distance" between measurements? Graphically speaking, I would need the area under the line chart, not just the sum of the values.

Rob Purser
Natick, MA

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August 25, 2015 - 8:10 pm
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I have a similar channel. You can do this in a MATLAB Analysis function:

% Get the data
[data,ts] = thingSpeakRead(32188,'NumMinutes',60);

% Calculate the number of minutes for each value (the weight)
weights = minutes(diff(ts));

% Discard the last data point (because you don't know its weight)
data(end) = [];

% Need to use "dot product" operator (.*), since MATLAB default is
% "cross product" operator.
sum(data .* weights)

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