How to index something based on numbering order???

Hi everyone

I am not that much professional in Matlab and I have a vector of x= 94*1 containig 7 different integer numbers (1 to 7). I want to generate another vector Y= 94*7 of random numbers between 0 and 1 and put them as a vector based on the number in the x vector. I will explain how...

for example if the first number in the vector x is 2, okay, that means the first row in the generated vector Y should be [0.02 0.82 0.0025 0.03, 0.0027, 0.0025 0.0015] the most imprtant thing is the all generated numbers should be between 0 and 1, and the max number should be located in the place of the number in the vector x.

this id the input: x = [2; 3; 7; 5; 1]

the expected output is: Y =

0.0200 0.8200 0.0025 0.0300 0.0027 0.0025 0.0015

0.0024 0.0035 0.7600 0.0080 0.0500 0.0014 0.0020

0.0200 0.0025 0.0300 0.0027 0.0250 0.0015 0.8900

0.0024 0.0035 0.0080 0.0500 0.8400 0.0020 0.0027

0.9120 0.0002 0.0050 0.0258 0.0020 0.0010 0.0000

Thanks in advance

Answer 1

[Guillaume]

Here is one way:

%input
x = [2; 3; 7; 5; 1] 

%generate random matrix without worrying about the order
A = rand(size(x, 1), max(x));
%find current location of max of each row:
[~, col] = max(A, [], 2);
%convert col and x to linear indices, which will indicate which elements to swap
source = sub2ind(size(A), (1:size(A, 1))', col);
dest = sub2ind(size(A), (1:size(A, 1))', x);
%swap current max with its intended location
A([source, dest]) = A([dest, source]);

Note that if you are on R2019a or later, with the 'linear' option for max, you can replace the two lines:

[~, col] = max(A, [], 2);
source = sub2ind(size(B), (1:size(A, 1))', col);

by

[~, source] = max(A, [], 2, 'linear');

[Gadelhag M Omar Mohmed]

Hi Guillaume

Thanks a lot for answering my question, I still have an error in the sample example you gave, which is: Undefined function or variable 'B'.

So, what is the variable B?

Regards

[Guillaume]

B was supposed to be A all along. No idea what was going through my head!

[Gadelhag M Omar Mohmed]

Hi Guillaume

Thank you, it is working as I want now. One more little question please, If I want to do the same process, but I want to have the total sum of the generated numbers that we generated in (A = rand(size(x, 1), max(x));) to be 1. So, I want the sum of these random numbers is 1.

Regards

[Guillaume]

A = A ./ sum(A, 2)

will normalise the rows of A so their sum is 1.