Extract a sub-matrix if the first or second column contains a specific number

I have a large matrix A, I want to extract submatrices B1, B2.. etc that contains the same number of columns as in A but only rows for which the first or second columns of A contains a specific number. For instance for this A matrix;

A=[1  4  0  0.0576  0  250  250  250;
4  5  0.017  0.092  0.158  250  250  250;
5  6  0.039  0.17  0.358  150  150  150;
3  6  0  0.0586  0  300  300  300;
6  7  0.0119  0.1008  0.209  150  150  150;
7  8  0.0085  0.072  0.149  250  250  250;
8  2  0  0.0625  0  250  250  250;
8  9  0.032  0.161  0.306  250  250  250;
9  4  0.01  0.085  0.176  250  250  250
]

Extract B such that it contains rows for which column 1 and column 2 in A contain the number '4' B4 should look like this

B4=[1  4  0  0.0576  0  250  250  250;
4  5  0.017  0.092  0.158  250  250  250;
9  4  0.01  0.085  0.176  250  250  250;
]

I have very huge matrices, I am wondering if there is a super efficient way to do this.

Answer 1

[Andrei Bobrov]

ii = 4;

Bii = A(any(A == ii,2),:);

[puttogether]

Thanks for the response Andrei. So am actually trying to create multiple matrices using a loop for example I want B1 to be a submatrix having 1 in either column 1 or column 2, B2 for 2 all the way through 9 for the example above. A very straight forward way to create submatrices B1 through B9. Thanks for your assist again

[puttogether]

So I decided to do this to create a cell array

for ii = 0:9; B{ii+1} = Branch(any(Branch == ii,2),:) end

But for some reason when the loop is at 1 I get the entire matrix A as the submatrix B1. Any idea on how to fix this?

[Andrei Bobrov]

[ii,jj] = find(squeeze(any(A == reshape(0:9,1,1,[]),2))); % R2016b and later
[ii,jj] = find(squeeze(any(bsxfun(@eq,A,reshape(0:9,1,1,[])),2))); % R2016a and earlier

B = accumarray(jj,ii,[],@(x){A(x,:)});

[puttogether]

Thank you!!!

[puttogether]

Is there a way to only search the first 2 columns. For instance searching for 1 in the following matrix returns the entire matrix yet am only interested in a submatrix which contains 1 in only column 1 and 2 (should return just the first row)

1 4 0 0.0576 0 250 250 1 4 5 0.017 0.092 0.158 250 250 1 5 6 0.039 0.17 0.358 150 150 1 3 6 0 0.0586 0 300 300 1 6 7 0.0119 0.1008 0.209 150 150 1 7 8 0.0085 0.072 0.149 250 250 1 8 2 0 0.0625 0 250 250 1 8 9 0.032 0.161 0.306 250 250 1 9 4 0.01 0.085 0.176 250 250 1

[puttogether]

Never mind I figured it out. Thanks for all the assist!!

[Andrei Bobrov]

[ii,jj] = find(squeeze(any(A(:,1:2) == reshape(0:9,1,1,[]),2))); % R2016b and later
B = accumarray(jj,ii,[],@(x){A(x,:)});