How to reduce vectors sizes if an element in a parent vector equals to zero without accessing for loop

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George Ansari 2017-8-7

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https://ww2.mathworks.cn/matlabcentral/answers/351889-how-to-reduce-vectors-sizes-if-an-element-in-a-parent-vector-equals-to-zero-without-accessing-for-lo

评论： George Ansari 2017-8-8

采纳的回答： Chad Greene

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Dear all,

I have the following code, is there a way to do the same thing but without for loop?

P_max = [100 150 200];
B = [1 2 3];
Pg = [90 150 150];
P=P_max - Pg;
for i=1:length(P_max)
    if (P(i) == 0)
       B(:,i) = [];
       Pg(:,i) = [];
       P_max(:,i) = [];
    end
end

Thanks! George.

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Answer 1

Chad Greene 2017-8-7

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Hi George,

Yes, there's a very efficient way to do this in Matlab without loops. Get the indices of all P = 0 like this:

ind = P==0;

Then remove the corresponding elements in B, Pg, and P_Max like this:

B(ind) = [];

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Chad Greene 2017-8-7

A small note: You're doing a good thing by removing the loop in this case. But when you do need to use loops, try not to use the variable i or j, because they're both built-in variable names in Matlab meaning sqrt(-1). Instead, it's common practice to use for k = ...

George Ansari 2017-8-8