how can I find a specific data in time table in matlab?

Asked by Hamed Hedayatnia on 17 Oct 2019

Latest activity Edited by Andrei Bobrov on 18 Oct 2019

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I am trying to extract the freez-thaw cycles in a timetable.freezing of stone only occur when the temperature drops below−3 °C in a day and thawing when temperature rises above 1 °C in next day. My quastion is that how can I define a function for it and then retime the time table based on it.

I need to find the days with mean temperature below−3 °C, followed by a day with mean temperature above 1 °C.(meteorological data file in attachment.)

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MATLAB

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R2018b

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Answer by Andrei Bobrov on 17 Oct 2019

Edited by Andrei Bobrov on 18 Oct 2019

Accepted Answer

i = diff(3*(data_mean_daily.tabrizmat7 < -3) + (data_mean_daily.tabrizmat7 > 1)) == -2;
T_out = data_mean_daily([i;false]|[false;i],:);

as at Sebastian:

i = (data_mean_daily.tabrizmat7(1:end-1) < -3) & (data_mean_daily.tabrizmat7(2:end) > 1);
T_out = data_mean_daily(find(i(:)')+[0;1],:);

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Hamed Hedayatnia on 18 Oct 2019

Dear Andrei.

Yes,it give the correct answer but in result both of ddays are appeared.i.e: if 18th january temp increrase to above +1 and the day before is -3, in result(which the number of days are important) both of them are appeared. So we can see coupled days for each result. another question(since I wanna learn for my next tries): why did you multiply first value by 3(*3)?

Hamed Hedayatnia on 18 Oct 2019

one more q: how can I compare the day with the day before?

Andrei Bobrov on 18 Oct 2019

k = 3*(data_mean_daily.tabrizmat7 < -3) + (data_mean_daily.tabrizmat7 > 1);

k is the vector of days, if the element has a value of 3, then the temperature of this day is less than -3, if the value is 1, the temperature is more than +1. We are looking for a combination in our case [3; 1] or diff([3;1]).

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Answer by Sebastian Bomberg on 17 Oct 2019

You can offset temperature by one day and compare against >= 4.

idx = data_mean_daily.tabrizmat7(1:end-1) >= 2 & ...    % temp at current day greater 2 AND
    data_mean_daily.tabrizmat7(2:end) >= 4;             % temp at next day greate 4
data_mean_daily(idx,:)

idx has one row less than data_mean_daily but the missing last row will be treated as false anyway.

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Andrei Bobrov on 18 Oct 2019

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MATLAB

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R2018b

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