## how to combine 2 matrix at once with loop process..?

on 3 Apr 2013

### Andrei Bobrov (view profile)

I have a hard case (in my opinion), and i need your favor for this thing..

I have a data like below :

```data = [1   0
2   0
3   0
4   0
5   0
6   0
7   0
8   0
9   0
10  0
11  0
12  0
13  0
14  0
15  0
16  0
17  0
18  0
19  0
20  0];
```

And 2 matrix like below :

```A =
```
```    11     3
17     1
5    19
6    18
6    16
18     7
11    15
14    13
4     2
20     4```

B =

```    4.0078    1.9147
4.9880    1.8967
1.7225    1.1802
1.1200    3.1427
2.6425    4.9374
2.4181    4.8850
3.6921    2.9100
3.0406    4.6255
3.5859    4.3326
2.4275    3.6506```

I want to change the value in matrix 'data' row 2 with matrix B, the changes according to the matrix A. Matrix A use as a number that will synchronize with matrix 'data' row 1. For example, let see the first line of matrix A and matrix B. In matrix 'data' row 2 the value in line 11 and 3 (elements of matrix A) will change from 0 to 4.0078 and 1.9147 (elements of matrix B), so the matrix data will change like below :

```data = [1   0
2   0
3   1.9147
4   0
5   0
6   0
7   0
8   0
9   0
10  0
11  4.0078
12  0
13  0
14  0
15  0
16  0
17  0
18  0
19  0
20  0     ];
```

The changes will looping per line of matrix A and B, so the results will generates 10 different matrix data combination. I already tried to coding it, but there’s still wrong and I stuck with it. My coding shown below :

```A = zeros(10,2);
B = zeros(10,2);
```
` for C = 1:10,`
```    d = 20;
a = randperm(d);
a = a(1:2);
A(C,:) = a;```
```    b = (1+(5-1).*rand(1,2));
B(C,:) = b;```
` end`
``` for C = 1:10
for i1 = 1:size(a),
for i2 = 1:size(b),
index = a(i1);
if data(index, 2) == 0
data(index, 2) = b(i2);
end
end
end
end```

Thank you..

Matt Kindig

### Matt Kindig (view profile)

on 3 Apr 2013

How do you handle the case where A has repeated indices, but B does not have repeated values? For example, in your shown data, the A(4,1) and A(5,1) elements both =4, but B(4,1) ~= B(5,1).

Noru

### Noru (view profile)

on 5 Apr 2013

in my case above there's no problem with that, because line 4 and line 5 will applied in different matrix 'data'.

the problem is how to insert elements of matrix A and B per line to matrix 'data' so it will create 10 different matrix 'data' combination. one line for one matrix 'data'.

do you have any solutions..?

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### Andrei Bobrov (view profile)

on 5 Apr 2013
Edited by Andrei Bobrov

### Andrei Bobrov (view profile)

on 7 Apr 2013
```sa = size(A,1);
out = accumarray([A(:), repmat((1:sa)',2,1)],B(:),[size(data,1) sa]);
```

or

```sa = size(A,1);
sd = size(data,1);
out = zeros(sd,sa);
out(sub2ind([sd,sa],A,repmat(1:sa,2,1)')) = B;
```

```sd = size(data,1);
data = reshape(num2cell(permute(cat(3,repmat((1:sd)',1,sa),out),...
[1 3 2]),[1 2]),[],1);
```

Noru

### Noru (view profile)

on 6 Apr 2013

thank you for your help, your solution real close to my expectation but i want to separate each combination of matrix 'data' with loop operation, so there are 10 matrix 'data' and not merged into one matrix 'data'..

how to do that..?

thank you..

Andrei Bobrov

on 7 Apr 2013

Noru

### Noru (view profile)

on 16 Apr 2013

ok thank you sir...

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