How to make Linear Regression Graph with TimeSeries (obtained with WeatherData) data

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1

Hi! I’m doing a university paper on global warming and so I decided to use the Wolfram Language as a research tool, so I built a command that, given a city and two dates, would graph the temperature of the city between the two points of the given dates.

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As additional information, I decided to include a linear regression to the graph, so I investigated how to do it (I am relatively new in this language) and I tried to do it with easy data and it came out quite well, but when using it with the data obtained with WeatherData knowing that I am using days and years instead of numbers, I did not know how to make wolfram understand this as numbers to use the LinearModelFit function.

Before writing here I did my research here on a similar problem ( https://community.wolfram.com/groups/-/m/t/4705759 ), but the data used are of much smaller magnitude.

The things I have done so far is that I have isolated the temperature and the seconds in different lists, I have removed the unit from the temperature with QuantityMagnitude, then I have used Transpose to leave in format {x1,y2},{x2,y2}…

And, it doesn’t work. I don’t know why: the syntax seems to be the same as the base model of the Documentation Centre.

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Does anyone know how to do this? Thanks in advance!

2

Can’t post the notebook, so here are some additional images:

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3

Pablo,

maybe this approach might help (I choose a larger time interval to see the effect):

start = DateObject[{1975}, "Year"];
end = DateObject[{2022}, "Year"];
data0 = WeatherData[Entity["City", {"Nuuk", "Sermersooq", "Greenland"}], "Temperature", {start, end, "Day"}];
data1 = data0["Path"];
data2 = {#1, QuantityMagnitude[#2]} & @@@ data1;
lm = LinearModelFit[data2, t, t];
DateListPlot[data0, Epilog -> {Red, Line[{{start, lm[UnixTime@start]}, {end, lm[UnixTime@end]}}]}, GridLines -> Automatic, ImageSize -> Large]

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4

That is the answer! Thank you very much!

5

Pablo,

I made a mistake in my answer, sorry! - The last line should read:

DateListPlot[data0, Epilog -> {Red, Line[{{start, lm[AbsoluteTime@start]}, {end, lm[AbsoluteTime@end]}}]}, GridLines -> Automatic, ImageSize -> Large]

So, one should use AbsoluteTime[] (and not UnixTime[]).
(When one data point per year - and not per day - is used, this becomes obvious.) The result is now more plausible …

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6

If you want to know why your version failed, it is almost certainly the replacement of QuantityMagnitude[Missing[_]] by Nothing: this will make some of your entries either an empty list or a one-element list instead of a two-element list, so you no longer have a clean two-column matrix (which is what the error message is telling you).

Note also that when you constructed DataFinal, you put x and y backwards: time should the x, temperature the y.