Matching string from multiple arrays
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Kerstin Bergentz
le 8 Sep 2020
Réponse apportée : Steven Lord
le 17 Sep 2020
Hi,
I have three structures with time stamps (char arrays, eg '2016-11-02 10:00:00') and corresponding datapoints of significant wave heights (double), and these are of different length for the three structures so I cannot just concatenate them.
Basically I want to make a new array with only the datapoint values where the correcpodning time stamp exists in all three of my structures' time stamp field .
I've used ismember and matrix multiplication for just two of the structures (see below), but I realise that I still have values in the array I'm checking against that doesn't exist in the thing I'm checking, so I still have uneven lengths of the arrays. I have 163 triplets of stuctures to check, hence the 'i' to be able to run through all of them eventually.
Drifter_okera5 = ismember(cellstr(Drifters(i).ObsTimestamp), cellstr(era5(i).timestamp)); % check if what is in drifters are in era5
DrifterHsera5 = Drifter_okera5.*Drifters(i).Hs'; % Take the resulting logical matrix and multiply it with the drifter HS
DrifterHsok = DrifterHs(DrifterHs~= 0); %remove all the values that are now zeros, these do not have a matching era5 hs
Any tips are most welcome!
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Adam Danz
le 8 Sep 2020
Modifié(e) : Adam Danz
le 10 Sep 2020
Here's a demo that identies exact datetime matches. It assumes you've already converted the timestamps to datetime values instead of char using t = datetime(DateStrings,'InputFormat',infmt).
% Create demo data - all column vectors
A.timestamp = datetime(2020,1,1)+days(1:10)';
A.waveheight = rand(10,1);
B.timestamp = datetime(2020,1,1)+days(1:15)';
B.waveheight = rand(15,1);
C.timestamp = datetime(2020,1,1)+days(1:5)';
C.waveheight = rand(5,1);
% Find which datetime values *exactly* match in all 3 structures.
% dtInAll is a vector of datetime values that exist in all 3 strcutures.
dtInAll = intersect(intersect(A.timestamp,B.timestamp),C.timestamp);
Now you can get the indices of datetime matches for each structure and extract the waveheight values.
% waves is a nx3 matrix of waveheights where columns are defined by
% [A,B,C] structures and rows defined by deInAll.
waves = [A.waveheight(ismember(A.timestamp, dtInAll)), ...
B.waveheight(ismember(B.timestamp, dtInAll)), ...
C.waveheight(ismember(C.timestamp, dtInAll))];
Summarize the resuls in a table (or timetable)
T = table();
T.TimeStamp = dtInAll
T = [T, array2table(waves,'VariableNames',{'A','B','C'})];
% 5×4 table
% TimeStamp A B C
% ___________ _______ ________ _______
% 02-Jan-2020 0.94479 0.40391 0.64775
% 03-Jan-2020 0.49086 0.096455 0.45092
% 04-Jan-2020 0.48925 0.13197 0.54701
% 05-Jan-2020 0.33772 0.94205 0.29632
% 06-Jan-2020 0.90005 0.95613 0.74469
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Steven Lord
le 17 Sep 2020
If you have your data stored in timetable arrays, call synchronize with your three timetable arrays as input and specify the newTimeBasis input as 'intersection'.
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