Computing the median of a group except one member

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wy6622 2019-2-13

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评论： wy6622 2019-2-14

I have a dataset of a variable x for S seasons of the same J firms (not ordered). I'd like to compute for each firm in each season, the median of all other firms in that season. e.g. S=2, J=6, my dataset is

M=[1 2 3 6 5 4 2 3 4 1 5 6; 1 1 1 1 1 1 2 2 2 2 2 2; 2 4 6 5 7 8 3 7 5 7 5 3]'

First column is the firm index, second column the season, third column the x values for each firm in each season.

I am thinking something like

for i=1:size(M,1)/6
    for j=6*i-5:6*i
        M(j,4)=median(M(6*i-5:6*i,3));
    end
end

but with the index of M(:,3) inside median() somehow telling MATLAB to exclude the jth entry of M(:,3)?

Thank you!

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madhan ravi 2019-2-14

ok did you get the answer to your question since you accepted the answer ?

wy6622 2019-2-14

在 MATLAB Online 中打开

It works for the most parts except the step where it tries to assign the computed median to the corresponding firm. The "row=..." row below returns 0's as opposed to the desired index.

M=[1 2 3 6 5 4 2 3 4 1 5 6; 1 1 1 1 1 1 2 2 2 2 2 2; 2 4 6 5 7 8 3 7 5 7 5 3]';
M(:,4)=0; %create column of zeros
num_seasons = unique(M(:,2)); %num of seasons
num_f = unique(M(:,1)); %num of firms
for i = 1:numel(num_seasons) % for each season...
    season = M(M(:,2) == num_seasons(i),:); %matrix of season being iterated
    for j = 1:numel(num_f) % for each firm...
        med = median(season(not(season(:,1)==num_f(j)),3)); %median of OTHER firms for the season
        disp(['Firm: ' num2str(num_f(j)) ' Season:' num2str(num_seasons(i)),...
            ' Median: ' num2str(med)]);
        row = all(M(:,[1 2])==[num2str(num_f(j)) num2str(num_seasons(i))],2); %locate row where firm and season matches
        M(row,4) = med; %append the median to the corresponding row, 4th col
    end
end

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采纳的回答

Kevin Phung 2019-2-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/444865-computing-the-median-of-a-group-except-one-member#answer_360935

在 MATLAB Online 中打开

Hello!

Is this sort of what you're looking for?

M=[1 2 3 6 5 4 2 3 4 1 5 6; 1 1 1 1 1 1 2 2 2 2 2 2; 2 4 6 5 7 8 3 7 5 7 5 3]';
num_seasons = unique(M(:,2)); %num of seasons
num_f = unique(M(:,1)); %num of firms
for i = 1:numel(num_seasons) % for each season...
    season = M(M(:,2) == num_seasons(i),:); %matrix of season being iterated
    for j = 1:numel(num_f) % for each firm...
        med = median(season(not(season(:,1)==num_f(j)),3)); %median of OTHER firms for the season
        disp(['Firm: ' num2str(num_f(j)) ' Season:' num2str(num_seasons(i)),...
            ' Median: ' num2str(med)]);
    end
end

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Kevin Phung 2019-2-14

在 MATLAB Online 中打开

Just for the sake of following up with my mistake:

I made the mistake of converting the values into strings. row should have been:

row = all(M(:,[1 2])==[num_f(j) num_seasons(i)],2); %locate row where firm and season matches

so this should have worked:

M=[1 2 3 6 5 4 2 3 4 1 5 6; 1 1 1 1 1 1 2 2 2 2 2 2; 2 4 6 5 7 8 3 7 5 7 5 3]';
M(:,4)=0; %create column of zeros
num_seasons = unique(M(:,2)); %num of seasons
num_f = unique(M(:,1)); %num of firms
for i = 1:numel(num_seasons) % for each season...
    season = M(M(:,2) == num_seasons(i),:); %matrix of season being iterated
    for j = 1:numel(num_f) % for each firm...
        med = median(season(not(season(:,1)==num_f(j)),3)); %median of OTHER firms for the season
        row = all(M(:,[1 2])==[num_f(j) num_seasons(i)],2); %locate row where firm and season matches
        M(row,4) = med; %append the median to the corresponding row, 4th col
    end
end