Calculate monthly averages without reshaping

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aaron Harvey
aaron Harvey 2016-2-18
编辑： Stephen23 2016-2-24
i have a time series of data and i would like to calculate monthly averages but keeping the vector lengths the same. (the variables also contain many nans)
For example if i have a date vector (yyyymm):
date=
199901
199901
199901
199905
199905
200107
200107
200107
variable=
1
2
3
4
5
5
6
7
How can i get
variable_montlyav=
2
2
2
4.5
4.5
6
nan (or 6 i dont mind)
6
so that i can use my new montly averaged variable with some existing codes i have.
  1 个评论
Stephen23
Stephen23 2016-2-22
编辑：Stephen23 2016-2-24
What exactly do you mean by a "date vector"? In MATLAB the term "date vector" has a specific meaning, which is a numeric vector consisting |y,m,d,H,M,S.F] values. If your data really was a date vector, it would looks like this:
1999 1 1 0 0 0
1999 1 1 0 0 0
1999 1 1 0 0 0
1999 5 1 0 0 0
1999 5 1 0 0 0
2001 7 1 0 0 0
2001 7 1 0 0 0
2001 7 1 0 0 0

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采纳的回答

Stephen23
Stephen23 2016-2-22
编辑：Stephen23 2016-2-24
Note: this code works if date is a cell array of strings, and also if date is a numeric vector of values representing year and month.
date = {'199901','199901','199901','199905','199905','200107','200107','200107'};
variable = [1,2,3,4,5,5,6,7];
[~,~,idx] = unique(date);
tmp = accumarray(idx(:), variable, [], @mean);
tmp(idx)
creates this output:
ans =
2.0000
2.0000
2.0000
4.5000
4.5000
6.0000
6.0000
6.0000

更多回答（1 个）

Roger Wohlwend
Roger Wohlwend 2016-2-22
A = accumarray(date, variable, [], @mean);
MeanValues = A(date);
  1 个评论
Stephen23
Stephen23 2016-2-22
This is not a very memory-efficient solution, as it will create temporary arrays with more than 200000 elements in them. See my answer for a more memory-efficient solution.

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