split matrix in diffrent sizes matrixes according to indicies vector

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christine schaer
christine schaer 2019-9-25
评论： christine schaer 2019-9-26
I have a matrix A (7x2) and a vector B. B represents the row indicies, where i want the matrix A to be sprlit.
e.g.
A = [2 6; 4 3; 3 3; 2 8; 9 1; 3 4; 7 5] B=[2; 3; 6]
output should be
A1 = [2 6; 4 3]
A2 = [3 3]
A3 = [2 8; 9 1; 3 4]
A4 = [7 5]
Do you have an idea how it could be done?
Thank you for help.

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采纳的回答

Stephen23
Stephen23 2019-9-25
编辑：Stephen23 2019-9-25
Do NOT create numbered variables. Indexing is simpler and much more efficient.
You can use mat2cell to split the matrix up into a cell array:
>> R = diff([0;B;size(A,1)]);
>> C = mat2cell(A,R,2);
>> C{:}
ans =
2 6
4 3
ans =
3 3
ans =
2 8
9 1
3 4
ans =
7 5
and then you can trivially access the contents of that cell array using indexing:
https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html
E.g.:
>> C{2}
ans =
3 3
>> C{3}
ans =
2 8
9 1
3 4
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Stephen23
Stephen23 2019-9-26
编辑：Stephen23 2019-9-26
"I want to add a third row to each cell ..."
This is confusing, because in your example you are adding a third column, not a row. Remember that matrices are defined by rows*columns, and this is how MATLAB indexing works too: (rows,columns,pages,...)
https://www.mathworks.com/help/matlab/math/array-indexing.html
In any case, you can simply use a loop, e.g.:
for k = 1:numel(C)
C{k}(:,3) = cumsum(C{k}(:,2));
end
Giving:
>> C{:}
ans =
2 6 6
4 3 9
ans =
3 3 3
ans =
2 8 8
9 1 9
3 4 13
ans =
7 5 5
Or, if you really want to use cellfun, something like this:
>> F = @(m)[m,cumsum(m(:,2))];
>> C = cellfun(F,C,'uni',0);
>> C{:}
ans =
2 6 6
4 3 9
ans =
3 3 3
ans =
2 8 8
9 1 9
3 4 13
ans =
7 5 5

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更多回答（1 个）

the cyclist
the cyclist 2019-9-25
Stephen's solution is better, but I thought I would post this for loop version, which might be a bit clearer to you on what is happening:
A = [2 6;
4 3;
3 3;
2 8;
9 1;
3 4;
7 5];
B=[2; 3; 6];
C = [0; B; size(A,1)];
for nj = 1:numel(C)-1
An{nj} = A(C(nj)+1:C(nj+1),:);
end
I would also advocate using cell arrays rather than dynamically named variables.

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