Assigning or replacing elements of another array into an array based on indices

Question

Ali Tawfik 2020-6-3

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https://ww2.mathworks.cn/matlabcentral/answers/540962-assigning-or-replacing-elements-of-another-array-into-an-array-based-on-indices

评论： Ali Tawfik 2020-6-3

Hi,

I am trying to replace or assign elements into another array based on indices, I did it but only with only element, I can NOT replace or assign multiple elements

I am using index functions inclduing find but with multiple elements I can NOT.

clear all;
clc;
b = [0 0 45 -45 -45 45 90 90];
t_90_c=find(b==90);
t_0_c=find(b==0);
t_45_c=find(ismember(b,[45 -45]));
b_new=b;
b_new(t_90_c)=8;
%b_new(t_90_c,t_0_c,t_45_c) = [8 9 2] % If I use this line I got an error of subscripted assignment dimension mismatch.. 

I want the b_new = [ 9 9 2 2 2 2 8 8]

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Answer 1

Peter O 2020-6-3

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https://ww2.mathworks.cn/matlabcentral/answers/540962-assigning-or-replacing-elements-of-another-array-into-an-array-based-on-indices#answer_445310

Ali,

I suggest you use logical indexing for this instead of FIND. It's faster and a little cleaner.

Hope this helps!

b = [0 0 45 -45 -45 45 90 90];
% Assign each from a test condition.
% You can assign a scalar to multiple values at once.
b_new=b;
b_new(b_new==90) = 8;
b_new(b_new==0) = 9; 
b_new(abs(b_new)==45) = 2; % May have unexpected effects on complex qtys. Fine for real-valued.
b_new(b_new == 45 | b_new == -45) = 2; % This uses a compound OR operator to evaluate both +/-45 cases, or if you have two separate cases you want to match.