Question

I have a problem with removing surplus rows in the end of the matrix. In general, I need to remove rows that contain a specific elements in a specific column, without using a loop. It seems easy but I still keep on getting some weird outcomes.

For simple example, let’s have a 10×10 matrix A:

A=[1:10; 901:910; 201:210; 301:310; 701:710; 401:410; 601:610; 501:510; 801:810; 101:110];

And I want to remove (for better illustration just replace with ones) that rows from fourth to the last, whose third columns contain value higher than 600. Result should look like that:

|  1     2     3     4     5     6     7     8     9    10|
|901   902   903   904   905   906   907   908   909   910|
|201   202   203   204   205   206   207   208   209   210|
|301   302   303   304   305   306   307   308   309   310|
|  1     1     1     1     1     1     1     1     1     1|
|401   402   403   404   405   406   407   408   409   410|
|  1     1     1     1     1     1     1     1     1     1|
|501   502   503   504   505   506   507   508   509   510|
|  1     1     1     1     1     1     1     1     1     1|
|101   102   103   104   105   106   107   108   109   110|

My idea looks like that:

A(A(4:end,3)>600,:)=[1];

But the outcome is some nonsense matrix.

Thanks for your help!

Answer 1

 A([false(3,1);A(4:end,3)>600],:)=1;

and as @yoda said, to remove the rows do:

 A([false(3,1);A(4:end,3)>600],:)=[];