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How to find compare unequal size matrices and create new matrix by combining them??

Asked by Iro on 6 May 2013

Hi, I have the following matrices:

```X = [1001 1011 1001 10 130 0.8 0.2;
1001 1012 1001 11 150 0.2 0.8;
1001 1012 1001 11 131 0.5 0.5;
1001 1012 1002 11 140 0.6 0.4];
```
```Y = [1001 1011 1001 10 112 1 122 214;
1001 1011 1001 11 221 1 134 113; % extra row
1001 1012 1001 11 98 1 58 82;
1001 1012 1001 11 68 1 59 67;
1001 1012 1002 11 32 1 56 98;
1004 1012 1005 12 67 1 89 132]; % extra row
```

and I want to get this :

```M = [1001 1011 1001 10 130 0.8 0.2;
1001 1011 1001 11 NaN NaN NaN; % or sth equivalent to NaN
1001 1012 1001 11 150 0.2 0.8;
1001 1012 1001 11 131 0.5 0.5;
1001 1012 1002 11 140 0.6 0.4;
1004 1012 1005 12 NaN NaN NaN];
```

I have difficulty in finding/comparing 4 elements together of every row (M(:,1:4)), and also when the size of the matrices in not equal...

Any suggestions on which could be the right function to solve it??

Thanks,

Iro

Iro on 7 May 2013

Is there any way to do it (or something similar) with

` find `

and/or

` ismember ? `

Any other suggestions?

Sean de Wolski on 7 May 2013

I'm not clear on how you derived M. Can you be very specific, where does each row in M come from?

Iro on 7 May 2013

M is the result I want to get with some function, derived from X an Y. More specifically, the four first columns come from Y's first 4 columsn while the rest 3 columns come from X's last three columns, in the case where the combinations of the first 4 column of Y are the same with combinations of X's first 4 columns... e.g: if M(i,1:4) is the same to any of X(j,1:4), then assign elements of X(j,5:7) to the M(i,5:end) by discarding the existing ones..

Let me know if it makes more sense now...Thanks!! :)

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Answer by Andrei Bobrov on 7 May 2013
```ii = ismember(Y(:,1:4),X(:,1:4),'rows');
M = [Y(:,1:4),nan(size(Y,1),3)];
M(ii,5:end) = X(:,5:end);
```

Iro on 9 May 2013

and what about when I have multiple rows with the same (r,1:4) combinations in Y? For example:

```X = [1001 1011 1001 10 130 0.8 0.2;
1001 1012 1001 11 150 0.2 0.8;
1001 1012 1002 11 131 0.5 0.5;
1001 1013 1002 11 140 0.6 0.4];
```
```Y = [1001 1011 1001 10 112 1 122 214;
1001 1011 1001 11 221 1 134 113; % extra (r,1:4) combination
1001 1011 1001 11 221 1 115 112; % extra multiple comb
1001 1012 1001 11 98 1 58 82; % multiple existing comb
1001 1012 1001 11 98 1 35 72; % multiple existing comb
1001 1012 1001 11 98 1 68 62; % multiple existing comb
1001 1012 1002 11 68 1 59 67;
1001 1013 1002 11 32 1 56 98;
1004 1012 1005 12 67 1 89 132]; % extra comb
```

I tried with

```[tf,loc] = ismember(Y(:,1:4),X(:,1:4),'rows')
M = [Y(:,1:4),nan(size(Y,1),3)];
M(tf,5:end) = X(loc,5:end);
```

in order to get this:

```    M = [1001 1011 1001 10 130 0.8 0.2; % taken from X(1,5:end)
1001 1011 1001 11 nan nan nan;
1001 1011 1001 11 nan nan nan;
1001 1012 1001 11 150 0.2 0.8; % taken from X(2,5:end)
1001 1012 1001 11 150 0.2 0.8; % taken from X(2,5:end)
1001 1012 1001 11 150 0.2 0.8; % taken from X(2,5:end)
1001 1012 1002 11 131 0.5 0.5; % taken from X(3,5:end)
1001 1013 1002 11 140 0.6 0.4; % taken from X(4,5:end)
1004 1012 1005 12 nan nan nan]; % ```

but I get the error:

```??? Subscript indices must either be real positive integers or logicals.
```

in the last line of my code.

Iro on 9 May 2013

Well I tried it with:

```M(tf,5:end) = X(loc(tf),5:end);
```

instead, and it seems to work. However I don't really understand what is the difference between loc and loc(tf) in relation to the error above (real positive integer or logical)... any hints?

Andrei Bobrov on 10 May 2013

All right, use loc(tf) instead loc, because loc has nulls and is non logical type.