# Replacing same rows with same variables in first to third column

3 views (last 30 days)
mr mo on 21 Dec 2017
Commented: Stephen Cobeldick on 21 Dec 2017
Hi. I have two matrices named aa and m.
aa=[1 2 3 7
4 5 6 8
7 8 9 9
3 2 3 8
6 5 6 7
7 8 7 9];
mm=[1 2 3 5
4 5 6 9
7 8 9 6];
I want to replace the rows of aa with the rows of m that have the same values in first to third column.
How can I do that?
Thanks a lot.

Image Analyst on 21 Dec 2017
What if m is
mm=[1 2 3 5
1 2 3 9
4 5 6 9
7 8 9 6];
Which row of m, the first or the second, should replace the first row of aa?
mr mo on 21 Dec 2017
In my case there are only one same rows in ‘aa’ and ‘mm’

Jos (10584) on 21 Dec 2017
No need for loops at all! Use both outputs of ismember and replace accordingly
aa = [1 2 3 7
4 5 6 8
7 8 9 9
3 2 3 8
6 5 6 7
7 8 7 9
1 2 3 999];
mm = [1 2 3 5
4 5 6 9
7 8 9 6];
[tf,loc] = ismember(aa(:,1:3),mm(:,1:3),'rows')
% tf indicates which rows in aa are found where (loc) in mm (only for columns 1-3)
aa(tf,:) = mm(loc(tf),:) % replace those rows

#### 1 Comment

Stephen Cobeldick on 21 Dec 2017
+1 the simplest is the best.

KSSV on 21 Dec 2017
Edited: KSSV on 21 Dec 2017
aa(1:3,1:3) = mm(1:3,1:3) ;

#### 1 Comment

mr mo on 21 Dec 2017
Thanks but this codes lost the fourth column values of mm.