# How to calculate circular mean every 8 cells?

조회 수: 2 (최근 30일)
Yoni Verhaegen -WE-1718- 2022년 6월 3일
답변: Star Strider 2022년 6월 3일
Hi all,
I have a dataset with wind directions at 3-hourly time steps and I would like to calculate daily average wind directions. I am, however, stuck. I got this (with dir = the wind direction in degrees, 0 to 360):
dir = accumarray(ceil((1:numel(dir))/8)',dir(:),[],@mean);
This, however, does not take into account the circular nature of the values. How can I do this?
I attach a small sample of the data (year - month - day - hour - wind direction):
2020 4 1 0 77.0016556593828
2020 4 1 3 61.6846224380681
2020 4 1 6 31.4624383596130
2020 4 1 9 35.1994739111645
2020 4 1 12 56.7123189304487
2020 4 1 15 337.212660715222
2020 4 1 18 332.720394142200
2020 4 1 21 359.309990882483
2020 4 2 0 1.81332665386765
2020 4 2 3 316.084846935155
2020 4 2 6 297.362308097189
2020 4 2 9 286.447414863766
2020 4 2 12 253.377128455776
2020 4 2 15 272.755841963236
2020 4 2 18 283.300130880562
2020 4 2 21 305.805458428448
2020 4 3 0 303.435585960465
2020 4 3 3 305.408085546923
2020 4 3 6 314.945219141016
2020 4 3 9 301.363197206495
2020 4 3 12 297.344102342364
2020 4 3 15 294.845524112617
2020 4 3 18 301.544742721005
2020 4 3 21 320.320593041074

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### 채택된 답변

Star Strider 2022년 6월 3일
One option would be to ‘decompose’ the angles into their ‘x’ and ‘y’ components, calculate the means of those, and then use atan2 to return the result —
D = [2020 4 1 0 77.0016556593828
2020 4 1 3 61.6846224380681
2020 4 1 6 31.4624383596130
2020 4 1 9 35.1994739111645
2020 4 1 12 56.7123189304487
2020 4 1 15 337.212660715222
2020 4 1 18 332.720394142200
2020 4 1 21 359.309990882483
2020 4 2 0 1.81332665386765
2020 4 2 3 316.084846935155
2020 4 2 6 297.362308097189
2020 4 2 9 286.447414863766
2020 4 2 12 253.377128455776
2020 4 2 15 272.755841963236
2020 4 2 18 283.300130880562
2020 4 2 21 305.805458428448
2020 4 3 0 303.435585960465
2020 4 3 3 305.408085546923
2020 4 3 6 314.945219141016
2020 4 3 9 301.363197206495
2020 4 3 12 297.344102342364
2020 4 3 15 294.845524112617
2020 4 3 18 301.544742721005
2020 4 3 21 320.320593041074];
dir = D(:,5);
meandir = @(a) atan2d(mean(sind(a)),mean(cosd(a)));
dir = accumarray(ceil((1:numel(dir))/8)',dir(:),[],meandir)
dir = 3×1
27.0977 -64.0652 -55.1192
dir = wrapTo360(dir) % Mapping Toolbox Function
dir = 3×1
27.0977 295.9348 304.8808
.

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