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Add data of a matrix based on an other matrix

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Philipp Wirtz
Philipp Wirtz 2018-5-11
评论： Philipp Wirtz 2018-5-11
I would like to add a certain amount of data points of one matrix in a new matrix, based on a third matrix. It is because I need to add data points from one day (it is not predefined how many datapoints there are going to be) and then go to the next day and do the same. This is the code I tried for now.
if true
% code
A = [1 1 1 2 2 2 3 4 5 6 6 6 7 8 9 10]; % Matrix that tells from which day data point of B is
B = rand(1,16).*100; % random data times 100 to get bigger numbers
i = 1; % variable used in the while loop
j = 1; % variable used in the while loop
C = []; % new matrix to store the summed data points for each day (it should become a 1x10 matrix in this specific case
while A(i) == i
while A(i) == i
C(1,i) = C(1,i) + B(1,j)
j = j + 1;
end
i = i + 1;
end
end
Hoping to find an answer. - Philipp

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采纳的回答

Stephen23
Stephen23 2018-5-11
编辑：Stephen23 2018-5-11
Loops are not required. One easy way would be to use accumarray:
>> A = [1 1 1 2 2 2 3 4 5 6 6 6 7 8 9 10];
>> B = rand(1,16);
>> C = accumarray(A(:),B(:))
C =
1.090191
1.127991
0.044079
0.483190
0.890956
0.136439
0.025175
0.364094
0.165231
0.917592
>> size(C)
ans =
10 1
For MATLAB releases >= R2015b you could use splitapply.

更多回答（2 个）

Ameer Hamza
Ameer Hamza 2018-5-11
splitapply(@sum, B, A)
Cathal Cunningham
Cathal Cunningham 2018-5-11
Use logical indexing to do this
% Pre-build array
C = zeros(1,size(unique(A),2));
for i = 1:length(C)
C(i) = sum(B(A==i));
end

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