Aggregate functions on grouped data

Question

Muneer 2014-2-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/119073-aggregate-functions-on-grouped-data

评论： Akhila 2022-9-20

Hello, I have three columns of data like this

The third column has values that repeat (entire column is in ascending order) and I would like to do operations on the first and second column based on the groups specified by the third column.

For example, in the third column, the first 4 values are 111, the next 5 are 166. This means one group is the first four values, and the second group is the next 5 values (denoted by number). So I would like to find the maximum of the first group in the first column and the min of the first group in the second column. My output would look like this:

max  min  sequence
8  111
2  166
0  200
2  250
1  275
5  300

The whole set is about 11 mil rows that would reduce to a smaller set. The problem is the groups or sequences are not the same number of rows. Any help would be greatly appreciated. Max and min aren't the only operations I'd like to do, but they illustrate the idea.

Thanks for your help.

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Answer 1

Dishant Arora 2014-2-25

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https://ww2.mathworks.cn/matlabcentral/answers/119073-aggregate-functions-on-grouped-data#answer_126113

编辑：Dishant Arora 2014-2-25

在 MATLAB Online 中打开

[b, ~, n] = unique(yourArray(:,3) , 'first');
firstColumn  = accumarray(n , yourArray(;,1) , size(b) , @(x) max(x));
secondColumn = accumarray(n , yourArray(;,2) , size(b) , @(x) min(x));
outputArray  = cat(2 , firstColumn , secondColumn , b);

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Muneer 2014-2-28

在 MATLAB Online 中打开

Can this be used on data that isn't a cell array of strings? In a previous step, I do this process

   segarray = textscan(fid, FormatString, block_size, 'delimiter',char(9));   
     for i = 1 : 5(segarray);
      segarray{i} = str2double(segarray{i}) ;  
      isn = isnan(segarray{i}) ;
      segarray{i}(isn) = 0 ;
     end

In order to find "NULL" values and replace them with zero. However, I think this is why I am having an error with the function you suggested (unique).

Akhila 2022-9-20

Remove the second input argument to the month function in line 2 of the script. The bar graph will now have month numbers in ascending order on the x-axis.

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