Copy certain number from one matrix to another

I have a matrix that i import from xlxs file using the code

function[output] = second()

    [raw] = xlsread('errors168h.xlsx');
    disp(raw)
    A = raw(:,1);
    B = raw(:,2);
    output=[A,B];

   end

and the matrix i got is

A  B
1  1
2  1
3  1
4  2
5  2
6  2
7  1
8  1
9  2
10  2
11  2

How can i copy matrix from second column but only certain number? the other number will be random either 1 or 2. Example

A  B      |     | A  B
1  1  1   |     | 1  1  1
2  1  1   |     | 2  1  1
3  1  1   |     | 3  1  1
4  2  2   |     | 4  2  2
5  2  1   |  OR | 5  2  2
6  2  1   |     | 6  2  1 
7  1  1   |     | 7  1  1
8  1  1   |     | 8  1  1
9  2  2   |     | 9  2  2
10 2  2   |     |10  2  1
11 2  1   |     |11  2  1

If the third row of 2 become 1, the rest of the column will become 1. process repeat until it reach another set of 2. Whenever it read number 1 on column B, it will stop processing and when it will start changing number again when it read 2 on column B. In short, it do like this

 A  B      A  B   C
------    -----------  
 1  1      1  1   1       %copy normally to C
 2  1      2  1   1
 3  1      3  1   1
 4  2      4  2   2       %read 2 at B. random 1 or 2. get 2
 5  2      5  2   1       %read 2 at B. random 1 or 2. get 1
 6  2      6  2   1       %read 2 at B. Follow previous value and set 1
 7  1      7  1   1       %read 1. copy normally value to C
 8  1      8  1   1
 9  2      9  2   1       %read 2 at B. random 1 or 2. get 1 (start process like previous)
10  2     10  2   1       %read 2 at B. Follow previous value and set 1
11  2     11  2   1       %read 2 at B. Follow previous value and set 1

[Massimo Zanetti]

I really don't get what you need to do.. can you try tyo explain better? What is the difference between the two matrices just above?

[Jane Mitchwell]

The first matrix is the result i got. I want to copy the first matrix, second column to a new column. However i want certain number only be copied to the new column. The number 2 also will be copied but at the same time, i want it to be random either still 2 or it change to 1. If lets say the second row of number 2 is change to 1, the rest of the rows will also change to 1

1    1
1    1
2    2
2    1
2    1
1    1

Answer 1

[Stephen23]

This does the job perfectly, without any explicit loop:

A = [1:12;1,1,1,2,2,2,1,1,2,2,2,1]'
idx = A(:,2)==2 & [true;diff(A(:,2))==1];
idy = ~idx(1)+cumsum(idx);
tmp = accumarray(idy,A(:,2),[],@(n){n});
fun = @(v)[sort(randi(1:2,nnz(v==2),1),'descend');v(v==1)];
out = [A,cell2mat(cellfun(fun,tmp,'UniformOutput',false))]

And tested a few times:

out =
   1     1     1
   2     1     1
   3     1     1
   4     2     2
   5     2     2
   6     2     2
   7     1     1
   8     1     1
   9     2     2
  10     2     2
  11     2     1
  12     1     1
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     2
   5     2     2
   6     2     1
   7     1     1
   8     1     1
   9     2     2
  10     2     1
  11     2     1
  12     1     1
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     1
   5     2     1
   6     2     1
   7     1     1
   8     1     1
   9     2     2
  10     2     1
  11     2     1
  12     1     1
out =
   1     1     1
   2     1     1
   3     1     1
   4     2     2
   5     2     1
   6     2     1
   7     1     1
   8     1     1
   9     2     2
  10     2     1
  11     2     1
  12     1     1
...etc

[Massimo Zanetti]

The trick to get idx is brilliant.

[Jane Mitchwell]

the code works. can u please explain a little bit about the coding?

[Stephen23]

@temp lover: the code with some notes:

A = [1:12;1,1,1,2,2,2,1,1,2,2,2,1]'
% locations of transition from 1 to 2:
idx = A(:,2)==2 & [true;diff(A(:,2))==1];
% identify groups of [2;2;..;2;1;1;...1]:
idy = ~idx(1)+cumsum(idx);
% split data into groups in a cell array:
tmp = accumarray(idy,A(:,2),[],@(n){n});
% function to create random twos and ones, with original ones at the end:
fun = @(v)[sort(randi(1:2,nnz(v==2),1),'descend');v(v==1)];
% Call function for each group in the cell array:
out = [A,cell2mat(cellfun(fun,tmp,'UniformOutput',false))]

If this answer resolves your question then please accept it.

[Jane Mitchwell]

Thank you for the explanation :)

[Jane Mitchwell]

If i want to insert a new value (1,2,3) instead just 1 and 2, which part of the code i need to change?

[Stephen23]

@Jane Mitchwell: The answer to your question is most likely "change the function fun". If you want more help than that then please explain exactly what you require, with input and output examples.

Answer 2

[Massimo Zanetti]

This version only requires one instance of ARRAYFUN

A = [1:12;2,1,1,2,2,2,1,1,2,2,2,1]';

I = (A(:,2)==2);
J = diff([0;I]);
E = I & J;
Z = cumsum(E)+~E(1);

C1 = accumarray(Z.*I+1,1); C1(1)=[];
C2 = accumarray(Z-Z.*I+1,1); C2(1)=[];

T = cell2mat( arrayfun( @(n) sort( [ randi(2,C1(n),1) ; ones(C2(n),1) ]  , 'descend' ) , (1:max(Z))' , 'UniformOutput', false) );

out = [A,T]

[Guillaume]

@Massimo, I think you should have preserved your original answer with a for loop.

At the end of the day, accumarray and arrayfun are loops. Yes, they're normally much faster than a for loop, but 3 of them, I'm not so sure anymore. Add to that an anonymous function call, plus a conversion from cell array to matrix and the new version might actually be slower.

The for loop was also a lot clearer. I love arrayfun (functional programming) but in this case, I think the for loop was neater.

[Massimo Zanetti]

Yes, you are right..

[Jane Mitchwell]

Out of curiosity, if i want to insert a new value (1,2,3) instead just 1 and 2, which part of the code i need to change?

Answer 3

[KSSV]

clc; clear all ;
A = [1  1
2  1
3  1
4  2
5  2
6  2
7  1
8  1
9  2
10  2
11  2];
% second row 
a = A(:,2) ;
a_rand = a(randperm(length(a)));
B = [A  a_rand]

Are you looking something like this?

[Jane Mitchwell]

Apparently the code above change the number 1 to number 2. i was hoping the number 1 remain the same. here is the output i got

     1     1     2
     2     1     1
     3     1     2
     4     2     1
     5     2     1
     6     2     2
     7     1     2
     8     1     1
     9     2     2
    10     2     1
    11     2     2

i try to change the code but i cant get the result like :

     1     1     1
     2     1     1
     3     1     1
     4     2     2
     5     2     2
     6     2     1
     7     1     1
     8     1     1
     9     2     2
    10     2     1
    11     2     1

Answer 4

[Andrei Bobrov]

out = A(:,[1,2,2]);
s = regionprops(bwlabel(A(:,2)-1),'PixelIdxList');
ii = {s.PixelIdxList};
jj = cellfun(@(ii)sort(randi(1:2,numel(ii),1),'descend'),ii,'un',0);
out(cat(1,ii{:}),3) = cat(1,jj{:});

[Jane Mitchwell]

Can explain abit about the codes? and if i wanted to add new value (3) instead just 1 and 2, which part do i have to alter?

[Andrei Bobrov]

Yes.

A = [1:12;1,3,3,3,2,7,2,1,2,2,2,1]'

out = A(:,[1,2,2]);
[~,~,c] = unique(A(:,2));
s = regionprops(c,'PixelIdxList');
ii = {s.PixelIdxList};
jj = cellfun(@(ii)sort(randi([1,A(ii(1),2)],...
                                          numel(ii),1),'descend'),ii,'un',0);
out(cat(1,ii{:}),3) = cat(1,jj{:});