Delete and merge rows and columns based on values of other matrix

suppose consider a matrix of A = [1 2 3 4 ; 5 6 7 8 ; 9 1 2 3 ; 1 2 3 4] consider matrix B = [ 1 0 2 4 ]

so in matrix B value of 2 unit is 0 so i need to delete second row and second column in matrix A

final A1 matrix = [1 3 4 ; 9 2 3 ; 1 3 4]

Answer 1

[Sindar]

If I understand correctly:

• You have one NxN matrix A
• And a second 1xN vector B
• When an element of B is zero, you delete rows and columns from A with the same index

A = [1 2 3 4 ; 5 6 7 8 ; 9 1 2 3 ; 1 2 3 4];
B = [ 1 0 2 4 ];
% find where B is nonzero
idx = find(B~=0);
% copy corresponding rows and columns of A to A1
A1=A(idx,idx);

[madhan ravi]

Without find() would result the same.

[vimal r]

can u tell me how to loop this..., suppose i have a matrix of B1 B2 B3....Bn condition is to check B1 if zero then eliminate the rows and columns in matrix A store as A1 then it should go to B2 check and store in A2 till An.

[Guillaume]

"suppose i have a matrix of B1 B2 B3 [..] store as A1 then [..] store in A2 till An"

That's a very bad idea and will complicates your code for no benefit. See Tutorial: Why Variables Should Not Be Named Dynamically to see the many problems with this design.

[vimal r]

d1 = readtable('d1.xlsx','Range','B1:AF32');
rd = readtable('randomnumberfinal.xlsx','Range','B2:AE55');
sen = rd(1,:);
% find where B is nonzero
idx = find(sen~=0);
% copy corresponding rows and columns of A to A1
A1=d1(idx,idx);

error

Undefined operator '~=' for input arguments of type 'table'.

Error in code1 (line 5)

idx = find(sen~=0);

[Guillaume]

If you're on R2019b or later, replace readtable by readmatrix so d1 and rd are matrices instead of tables. The rest of your code will then work properly.

Or in any version you can continue importing as a table but then you have to use the correct indexing to get data out of a table:

sen = rd{1, :};  %{} to extract data out of a table.

[vimal r]

so how to solve without looping it by individually...??

[Guillaume]

I'm not sure which of your 3 questions the above refers to. You would be better off starting a new question for each topic.