two matrix problem

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Mate 2u
Mate 2u 2012-6-20
Hi there, I have 2 matrixes of size 300x1.
One matrix A consists of 1's and -1's, and B consists of positive and negative numbers.
On matrix A we tend to see many 1's and -1's in a row. I want to run a program such that whenever the value of A remains 1 or -1 it does the cumsum of B....but then if the cumsum goes below some value of -0.2 the rest of the A values below will be zero till it changes to -1/1 and so on...
For example the input is
. A=[1; 1; 1; 1; 1; -1 ;-1 ;-1 ;1 ;1 ;1 ;1 ;1]
B=[0.4; -0.2; -0.2; -0.25; 0.6; -0.3; 0.4; 0.2; 0.5; 0.3; -0.8; -0.9; 0.9]
The output should be:
A= [ 1 1 1 1 0 -1 0 0 1 1 1 1 0]

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回答（3 个）

Andrei Bobrov
Andrei Bobrov 2012-6-20
A=[1; 1; 1; 1; 1; -1 ;-1 ;-1 ;1 ;1 ;1 ;1 ;1];
B=[0.4; -0.2; -0.2; -0.25; 0.6; -0.3; 0.4; 0.2; 0.5; 0.3; -0.8; -0.9; 0.9];
K = -.2;
T = cumsum([true;diff(A > 0) ~= 0]);
d = accumarray(T,B,[],@(x)find(cumsum(x) < K,1,'first'));
N = histc(T,unique(T));
out = A.*cell2mat(arrayfun(@(x,y)[ones(y,1);zeros(x-y,1)] ,N,d,'un',0));
Honglei Chen
Honglei Chen 2012-6-21
A=[1; 1; 1; 1; 1; -1 ;-1 ;-1 ;1 ;1 ;1 ;1 ;1];
B=[0.4; -0.2; -0.2; -0.25; 0.6; -0.3; 0.4; 0.2; 0.5; 0.3; -0.8; -0.9; 0.9];
bd = [1;find(diff(A))+1;numel(A)+1];
cell2mat(cellfun(@(x,y) [x(1:find(cumsum(y)<-0.2));...
zeros(numel(x)-find(cumsum(y)<-0.2),1)],mat2cell(A,diff(bd),1),...
mat2cell(B,diff(bd),1),'UniformOutput',false))
Jan
Jan 2012-6-21
And the dull loop:
A = [1; 1; 1; 1; 1; -1 ;-1 ;-1 ;1 ;1 ;1 ;1 ;1];
B = [0.4; -0.2; -0.2; -0.25; 0.6; -0.3; 0.4; 0.2; 0.5; 0.3; -0.8; -0.9; 0.9];
accum = 0;
pivot = A(1);
for i = 1:length(A)
if A(i) == pivot % same A value
if accum >= -0.2
accum = accum + B(i); % accumulation
else % lower limit was hit
A(i) = 0;
end
else % changed A value
accum = B(i); % reset accumulator
pivot = A(i); % remember new value
end
end

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