在Matlab中分組和彙總

Question

我有一個簡單的矩陣，在某些列中有重複值。我需要按名稱和星期分組數據，並總結每週給定的價格。這裏是例子：

name day week price 
John 12 12 200 
John 14 12 70 
John 25 13 150 
John 1 14 10 
Ann 13 12 100 
Ann 15 12 100 
Ann 20 13 50 

所需的輸出將是：

name week sum 
    John 12 270 
    John 13 150 
    John 14 10 
    Ann 12 200 
    Ann 13 50 

有沒有一個很好的辦法做到這一點？我用的循環，但不知道它是做的最好的方式：

names= unique(data(:,1)); % getting unique names from data 
n=size(names, 1);   % number of unique names 
m=size(data(:,1),1);  % number of total rows 
sum=[];     % empty matrix for writing the results 
for i = 1:n    
     temp=[];   % creating temporar matrix 
     k=1; 
    for j=1:m 
     if name(i)==data(j,1)  % going through all the rows and getting the rows of 
      temp(k,:)=data(j,:); % the same name and putting in temporar matrix 
      k=k+1; 
     end 
    end 
    count=0; 
    s=1; 
    for l = 1:size(temp,1)-1  % going through temporar matrix of one name(e.g.John) 
     if temp(l,3)==temp(l+1,3) % checking if the day of current row is equal to the 
     count=count+temp(l,4); % date of the next row (the data is sorted by name 
     else      % and date) and then summing the prices 4th column 
      sum(s, 1:3)=[names(i) temp(l,3) count]; 
      count=0;    % if the days are not equal, then writing the answer 
      s=s+1;    % to the output matrix sum 
     end   
    end 
end 

Answer 1

使用accumarray。它會分組和彙總這樣的值。您可以使用第三otuput參數從unique(data(:,1))得到的數字指標傳遞給的accumarray的subs說法。詳情請參閱doc accumarray。

Answer 2

也許最簡單的方法是使用GRPSTATS功能從統計工具箱。你必須在name和week以產生第一組結合：

[name_week priceSum] = grpstats(price, strcat(name(:), '@', week(:)), {'gname','sum'});