# Update elements in matrix with condition

4 次查看（过去 30 天）
Ravi Kumar2021-10-26

I have a large matrix (1st image). I need to update element in column 3&4 whenver it becomes 0 in column 5 or integer changes in column 6.
And I want to update it with sum from column 1 and 2.
See second image for more clarity. My matrix should perform this for all the rows. ##### 1 个评论显示隐藏 无
Ravi Kumar 2021-10-26
Tried this, but not working. (still getting same values in column 3&4)
N = size(P,1);
for i = 1:1:N
if P(N,5) == 0
P(N,3) = P(N,1) + P(N,3);
end
end

### 回答（2 个）

Rik 2021-10-26
N = size(P,1);
for k = 1:1:N
if P(k,5) == 0
P(k,3) = P(k,1) + P(k,3);
end
end
Similar code will allow you to edit when the value changes:
if k>1 && A(k-1)==A(k)
##### 0 个评论显示隐藏 -1更早的评论

Cris LaPierre 2021-10-26
Use logical arrays (Ch 12 of MATLAB Onramp).
Perhaps something like this (untested)
P(P(:,5)==0,3)=sum(P(P(:,5)==0,[1,3],2));
P(P(:,5)==0,4)=sum(P(P(:,5)==0,[2,4],2))

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