Mean data of each month (Data Matrix)

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Matlab_G
Matlab_G 2022-11-20
编辑： Campion Loong 2022-11-30
Hello,
I have a long data matrix with data from the year 2000 to 2010 of the following format (see picture below)
row 1= year
row2=month
row3=day of the month
row4=data
How can i calculate the average for each month of each year? (ie. each jan average, feb average, 10 march average.....)
Thanks in advance
  2 个评论
the cyclist
the cyclist 2022-11-20
编辑：the cyclist 2022-11-20
Do you want the average of all Januarys together, or January 2000 separate average from January 2001?
Also, when you say "data matrix", how is the data stored? From your screenshot, it looks like it might be a table. Can you upload the data?
Matlab_G
Matlab_G 2022-11-20
The data is all in a table yes.
I would need the seperate averages. ex: jan 2000 avg, jan 2001 avg, jan 2002 avg etc for each month

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回答（1 个）

the cyclist
the cyclist 2022-11-20
Here is one way:
% Create a table of pretend data, in your format
Var1 = [2000; 1; 1; 0.12];
Var2 = [2000; 1; 2; 0.13];
Var3 = [2000; 2; 1; 0.14];
Var4 = [2001; 1; 1; 0.15];
Var5 = [2001; 1; 2; 0.16];
Var6 = [2001; 2; 1; 0.17];
T = table(Var1,Var2,Var3,Var4,Var5,Var6);
% Because none of the variable label information is actually encoded in the
% table, convert to array, and then recast into meaningful column names.
% This is known as the "tidy" format.
A = table2array(T);
T2 = array2table(A','VariableNames',{'year','month','day','data'});
% Split-apply to get mean of each month
[G,TID] = findgroups(T2(:,{'year','month'}));
monthMean = splitapply(@mean,T2(:,'data'),G);
% Put it all together in a new table
output = [TID,table(monthMean)]
It is a bit awkward, but the primary reason for that awkwardness is that your data are not "tidy". Therefore, the vast majority of the code is actually getting the data into the format this is expected for most table operations (i.e. each column is a feature label, and each row is an observation).
If you can go back upstream and get your data into the format of my table T2 here, I would do that.
  1 个评论
Campion Loong
Campion Loong 2022-11-30
编辑：Campion Loong 2022-11-30
Ran in:
I agree with @the cyclist above, that it will be much more straightforward with your data in his T2 format. That said, using your initial data (), it will be cleaner with timetable
Resuse @the cyclist's pretended data:
Var1 = [2000; 1; 1; 0.12];
Var2 = [2000; 1; 2; 0.13];
Var3 = [2000; 2; 1; 0.14];
Var4 = [2001; 1; 1; 0.15];
Var5 = [2001; 1; 2; 0.16];
Var6 = [2001; 2; 1; 0.17];
T = table(Var1,Var2,Var3,Var4,Var5,Var6)
T = 4×6 table
Var1 Var2 Var3 Var4 Var5 Var6 ____ ____ ____ ____ ____ ____ 2000 2000 2000 2001 2001 2001 1 1 2 1 1 2 1 2 1 1 2 1 0.12 0.13 0.14 0.15 0.16 0.17
Put your timestamped data in a timetable:
% timestamps as datetime from rows in table T
timestamps = datetime(T{1,:}, T{2,:}, T{3,:});
TT = timetable(timestamps', T{4,:}') % note the transposes within
TT = 6×1 timetable
Time Var1 ___________ ____ 01-Jan-2000 0.12 02-Jan-2000 0.13 01-Feb-2000 0.14 01-Jan-2001 0.15 02-Jan-2001 0.16 01-Feb-2001 0.17
Get your monthly average in 1 line, using groupsummary:
groupsummary(TT, "Time", "month", "mean")
ans = 4×3 table
month_Time GroupCount mean_Var1 __________ __________ _________ Jan-2000 2 0.125 Feb-2000 1 0.14 Jan-2001 2 0.155 Feb-2001 1 0.17

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