how to extract similar columns from different matrices

Dear,

I have tow matrices with different size and I need to get the similar columns from the first on.

    a=[
       0     0     1     1     1     1     0     0     0     0     0     0   0     0
       1     1     1     0     0     0     0     0     0     0     0     0   0     0
       0     0     0     0     0     0     0     1     1     1     0     0   0     0
       0     0     0     0     0     0     0     0     0     1     1     1   1     0
       1     0     0     0     0     0     0     0     0     0     0     0   0     0
       0     0     0     0     0     0     0     0     0     0     0     0   1     1
       1     1     0     0     0     0     0     0     0     0     0     0   0     0]';

b=[
     0     0     1     1     1     1     1     1     1     1     1     0     0     0     0     0     0     0     0
     1     1     1     1     1     1     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     1     1     1     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     1     1     1
     1     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0
     1     1     1     1     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0]';

they have the same size of rows. I tried this

tf = ismember(C, a(ismember(a,b,'rows')), 'rows') 
result = C(tf,:)

I take the transpose for the matrices but there is an error, I used intersect command but is the same.

can anyone help me please I will be grateful.

regards,

Reway

Answer 1

[Guillaume]

Possibly, in your first expression you meant to have

a(ismember(a, b, 'rows'), :) %rather than a(ismember(a,b,'rows'))

But if you don't care about not getting the duplicate rows in a, then:

intersect(a, b, 'rows')

is simpler.

You haven't showed C in your example. Possibly, all you want is this:

result = intersect(C, intersect(a, b, 'rows'), 'rows')

Note that if you get an error, tell us what the exact error message is.

[rewayda mohsin]

Dear Guillaume,

There is no error, but I tried and I got

[ 0     0     1     1     1     1     1     1     1     1     1     0]';

for

b(ismember(a,b,'rows'))

why is the result like this I mean less than the number of the columns, could you please explain it to me and if I want to extract the columns from b what should I do there is no index.

Thank you for helping me.

regards

>>

 

[Guillaume]

As I showed in the very first line of my answer, you need to use:

b(ismember(a, b, 'rows'), :)

With your expression you're only asking for the first column of all the intersecting rows. You want all columns, hence you need to ask for them with the :

[rewayda mohsin]

Dear,

I used it thanks for your help. I used

a(ismember(a,b,'rows'),:)

it gave me the columns but without the index so how I going to extract them from a. could you suggest something for me please.

many thanks.

Reway

[Guillaume]

I don't understand what you're asking anymore. You've already extracted the columns from a.

If you want the indices from b, use the 2nd return value of ismember, or simply swap a and b in your expression.

[rewayda mohsin]

Dear Guillaume,

I used this

c=[  a(ismember(a, b, 'rows'),:)]'

and I got this columns

c=[ 1     1     1     1     0     0     1     0     0
     1     0     1     1     0     0     0     0     0
     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0
     0     0     0     0     1     0     0     0     0
     0     0     1     1     0     0     0     0     0];

its what I want exactly the columns from a inside b but I tried to find their index from matrix a so I can extract them from a but I couldn't.

what I want is to find the reminder of the matrix a after we check which column is member in b. I used

[i,j]=[a(ismember(a, b, 'rows'),:)]'

and I swapped a and b but no good result. I hope you understand me.

Thanks a lot for your answer.

Reway

[Thorsten]

To get the row index of all rows in a that also appear in b, use

 idx = ismember(a,b,'rows');

Now you use this logical row index and extract the corresponding rows from a:

 commonrows = a(idx, :);

You can write both commands in one line:

commonrows = a(ismember(a, b, 'rows'), :);

which is precisely what Guillaume suggested.

If that's not what you want, please try to rephrase your question.

[rewayda mohsin]

Thanks Thorsten,

I think yes Guillaume gave me what I asked exactly but I messed this

   idx = ismember(a,b,'rows');

I didn't notice its the index, I expected to get the index of the column in the matrix as a number of the column.

many thanks,

regards,