Mean of values in acolumn depending on VARYING values of another column

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Freya
Freya 2023-10-4
评论： Freya 2023-10-5
Hi, I would like to calculate the mean of values in a coulmn, based on the values in another column. However, different from other questions asked previously on this forum, the values in the second column I need to use are not specific, but change. Please see attached file and hopefully it will be easier to get what I mean. Maybe I need to use a for loop running through all the values of the second column? Thank you!

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Dyuman Joshi
Dyuman Joshi 2023-10-4
Ran in:
in =readmatrix('Book2.xlsx');
disp(in)
1 1 2 2 3 1 4 2 5 3 6 1 7 2 8 4 9 1 10 5 11 6 12 5 13 5 14 4 15 6 16 3 17 6 18 2 19 1 20 5 21 3 22 2 23 4
out = accumarray(in(:,2),in(:,1),[],@mean)
out = 6×1
7.6000 10.6000 14.0000 15.0000 13.7500 14.3333
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Dyuman Joshi
Dyuman Joshi 2023-10-5
Ran in:
Use the first output of unique()
format longg
in = readmatrix('Book3.xlsx');
[out1,~,idx] = unique(in(:,2))
out1 = 535×1
1.0e+00 * 1000227087 1000227106 1000594972 1000594973 1000594974 1000594975 1000594976 1000594977 1000594978 1000594979
idx = 13354×1
1 2 3 4 5 6 7 8 9 10
out2 = accumarray(idx,in(:,1),[],@mean)
out2 = 535×1
0.453491780924332 0.240638995346782 0.366433792273591 0.155783195173162 0.359111503883272 0.334567544249371 0.234826867085867 0.335793779361822 -0.0249592514078918 0.260758590555741
Concatenate them horizontally to get them in the same array
out = [out1 out2];

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Ken Garrard
Ken Garrard 2023-10-4
You do not need a for loop.
Assumming that your data is in an Nx2 variable named, mydata.
% Select rows matching criteria in column 2
% For example, values in column 2 greater than one and less than five
hits = mydata(:,2) > 1 & mydata(:,2) < 5;
% Mean of values from column 1
mean(mydata(hits,1))
ans =
12.7273

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