How to vectorize?

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pipin
pipin 2023-7-29
编辑： Bruno Luong 2023-8-2
Ran in:
Hi, is it possible to avoid the loop? Thanks.
x=(1:3:r);
Unrecognized function or variable 'r'.
[r,c]=size(Tr);
E1=zeros(r,c);
for i=1:c
E1(x,i)=E(Tr(r,i),i);
end
>> size(Tr)
ans =
21 6
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Image Analyst
Image Analyst 2023-7-29
Not seeing it. Again, what is Tr and E (not E1, but E)?
Does your for loop even work? What is the desired output?
If you have any more questions, then attach your data and missing code to read it in after you read this:
TUTORIAL: How to ask a question (on Answers) and get a fast answer
pipin
pipin 2023-7-29
thanks your help I made some mistakes while creating the code because it's a bit laborious. Here's the correct version
%input:
row=10;
columns=5;
step=3;
%%*************
E = round(rand(row,columns)*10)
Tr = randi(size(E,1),row,size(E,2))
[r,c]=size(Tr);
x=(1:step:r);
% Your method
E1=zeros(r,c);
for i=1:c
Tr(x,i)
E(Tr(x,i),i)
E1(x,i)=E(Tr(x,i),i);
end
E1

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采纳的回答

Bruno Luong
Bruno Luong 2023-7-30
编辑：Bruno Luong 2023-7-30
Just to pull out the right answer (my previous answer applied on a WRONG calculation specified by OP)
% vectorized method
c = size(Tr,2);
m = size(E,1);
x = 1:step:m;
E1 = zeros(size(Tr));
E1(x,:) = E(Tr(x,:) + (0:c-1)*m);
  2 个评论
pipin
pipin 2023-7-30
编辑：pipin 2023-7-30
hello.. why do you say that the previous answer was wrong? on the isequal test it was correct
(what is OP?)
Bruno Luong
Bruno Luong 2023-7-30
编辑：Bruno Luong 2023-7-30
OP is Original Poster, it's you who wrote : "excuse me.. z=r...i change it in code" ... remember?
My answer (not the comments below it) is wrong because the question is wrong.

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更多回答（1 个）

Bruno Luong
Bruno Luong 2023-7-29
编辑：Bruno Luong 2023-7-29
Ran in:
If you want obscure code by avoiding for-loop
E = rand(10,5)
E = 10×5
0.4433 0.5126 0.5907 0.7564 0.9740 0.9908 0.4916 0.9634 0.8613 0.0549 0.9769 0.2085 0.4765 0.2052 0.7497 0.0450 0.8816 0.9243 0.6475 0.1040 0.8076 0.1900 0.4109 0.6581 0.2044 0.4685 0.1936 0.7925 0.7647 0.4082 0.9868 0.9336 0.2478 0.0403 0.7413 0.1741 0.5068 0.1629 0.0827 0.0434 0.1120 0.7868 0.0827 0.4696 0.7350 0.4545 0.5871 0.0055 0.1273 0.2868
Tr = randi(size(E,1),9,size(E,2))
Tr = 9×5
9 10 5 2 4 9 10 9 9 2 1 10 4 6 2 2 8 2 3 4 8 2 7 9 8 5 7 2 4 5 5 5 7 9 5 5 10 10 4 3 9 8 3 3 7
[r,c]=size(Tr);
x=(1:3:r);
[r,c]=size(Tr);
x=(1:3:r);
% Your method
E1=zeros(r,c);
for i=1:c
E1(x,i)=E(Tr(r,i),i);
end
E1
E1 = 9×5
0.1120 0.5068 0.4765 0.2052 0.7413 0 0 0 0 0 0 0 0 0 0 0.1120 0.5068 0.4765 0.2052 0.7413 0 0 0 0 0 0 0 0 0 0 0.1120 0.5068 0.4765 0.2052 0.7413 0 0 0 0 0 0 0 0 0 0
% vectorized method
E1=zeros(r,c);
i=1:c;
E1(x(:) + (i-1)*r) = repmat(E(Tr(r,i) + (i-1)*size(E,1)),length(x),1);
E1
E1 = 9×5
0.1120 0.5068 0.4765 0.2052 0.7413 0 0 0 0 0 0 0 0 0 0 0.1120 0.5068 0.4765 0.2052 0.7413 0 0 0 0 0 0 0 0 0 0 0.1120 0.5068 0.4765 0.2052 0.7413 0 0 0 0 0 0 0 0 0 0
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Bruno Luong
Bruno Luong 2023-8-2
编辑：Bruno Luong 2023-8-2
Code to handle the case Tr == 0
c = size(Tr,2);
m = size(E,1);
x = 1:step:m;
E1 = zeros(size(Tr));
Trx = Tr(x,:);
iE = Trx + m*(0:c-1);
tmp = E(max(iE,1));
tmp(Trx == 0) = 0;
E1(x,:) = tmp;
it does not handle still the case Tr > m or Tr < 0.
If you havve data that are not valid for proper indexing it will be a mess to deal with.
pipin
pipin 2023-8-2
Correct..thank you!

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