Cumulative sum of groups

Question

PGrant 2018-4-25

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评论： PGrant 2024-6-3

I need the cumlative sum of the second column of Data grouped by (or reset at each change in) the first column of Data please:

Data = [[1;1;1; 2;2;2; 3;3;3], [1;0;1; 0;1;1; 0;1;0]]
Answer = [Data, [1;1;2; 0;1;2; 0;1;1]]
Data =
   1
   0
   1
   0
   1
   1
   0
   1
   0
Answer =
   1     1
   0     1
   1     2
   0     0
   1     1
   1     2
   0     0
   1     1
   0     1

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Stephen23 2018-4-25

编辑：Stephen23 2018-4-25

@PGrant: please explain the logic of how to calculate Answer: assume that we a stupid and that every step need to be shown to us.

PGrant 2018-4-25

Like a normal cumsum on column 2 of the Data with the difference being that it needs to restart for every change in column 1 of data resulting in column 3 of Answer. Columns 1 & 2 of Answer are just Data...

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Answer 1

Stephen23 2018-4-25

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编辑：Stephen23 2018-4-25

在 MATLAB Online 中打开

>> data = [1,1;1,0;1,1;2,0;2,1;2,1;3,0;3,1;3,0];
>> C = accumarray(data(:,1),data(:,2),[],@(v){cumsum(v)});
>> [data,vertcat(C{:})]
ans =
   1   1   1
   1   0   1
   1   1   2
   2   0   0
   2   1   1
   2   1   2
   3   0   0
   3   1   1
   3   0   1

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PGrant 2018-4-25

Thanks so much Stephen. Greatly appreciated!

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Answer 2

Lola Davidson 2024-6-3

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The grouptransform function was introduced in R2018b to help make problems like this a bit simpler. You can avoid the tricky cell array syntax that you need to use accumarray and just do this:

Data(:,3) = grouptransform(Data(:,2),Data(:,1),@cumsum)