We have a matrix containing the year month and day of data points. We want to find out how often each day occurs. Thanks in advance!

Question

Leon Garger 2016-12-12

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https://ww2.mathworks.cn/matlabcentral/answers/316584-we-have-a-matrix-containing-the-year-month-and-day-of-data-points-we-want-to-find-out-how-often-eac

回答： Star Strider 2016-12-12

We want to know how often a day repeats.

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Answer 1

Isabella Osetinsky-Tzidaki 2016-12-12

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编辑：Isabella Osetinsky-Tzidaki 2016-12-12

在 MATLAB Online 中打开

% A is N by 3 matrix (y,M,d)

B=datetime(A,'Format','yyyyMMdd');

C=char(B);

D=str2num(C);

F=unique(D);

L=length(F);

Answer=nan(L,2); % pre-allocate date and its occurrence columns

for i=1:L

    n=length(find(D==F(i)));
    Answer(i,:)=[F(i) n];

end

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Answer 2

Star Strider 2016-12-12

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https://ww2.mathworks.cn/matlabcentral/answers/316584-we-have-a-matrix-containing-the-year-month-and-day-of-data-points-we-want-to-find-out-how-often-eac#answer_246925

在 MATLAB Online 中打开

Another approach:

M = [2016 12 12;  2016 12 11;  2016 12 11;  2016 12 10];    % Create Data
dn = datenum( M );                                          % Compute Date Numbers
[Ud,ia,ic] = unique(dn, 'stable');                          % The 'stable' Argument Retains The Original Order
date_tally = accumarray(ic, 1);                             % Count Occurrences
Result = [M(ia,:), date_tally]
Result =
        2016          12          12           1
        2016          12          11           2
        2016          12          10           1