How to exclude rows on the basis of specific entries?

I have 260 rows and 16 columns with entries belong to {1,2,3,4}, I want to exclude those rows in which first four entries of each row is 4 , or in general how can I exclude rows on the basis of entries?

Answer 1

[Guillaume]

It's not clear what you mean by repeat.

If you mean you want to delete rows whose first four columns contain more than one 4:

A = [4 4 1 2; 4 4 4 4;1 4 2 4;4 2 3 2] 
todelete = sum(A(:, 1:4) == 4, 2) > 1;  
A(todelete, :) = []

If you mean you want to delete rows whose first four columns contain two more more consecutive 4, then it's a lot more complicated. One possible way

A = [4 4 1 2; 4 4 4 4;1 4 2 4;4 2 3 2] 
todelete = cellfun(@(row) ~isempty(strfind(row, [1 1])), num2cell(A(:, 1:4) == 4, 2));
A(todelete, :) = []

[Ammy]

Thank you very much. A = [4 4 1 2; 4 4 4 4;1 4 2 4;4 2 3 2]

todelete = sum(A(:, 1:4) == 4, 2) > 1;

A(todelete, :) = []

this works, But if I have 1000 rows and 16 columns and I want to delete all rows if any of the following holds:

1-There is more than one 4 in first four columns i-e (column 1 to column 4);

2-There is more than one 4 in column 5 to column 8;

3-There is more than one 4 column 9 to column 12;

4-There is more than one 4 in column 13 to column 16;

would you please help me.

[Guillaume]

assert(mod(size(A, 2), 4) == 0, 'Number of columns not a multiple of 4')
todelete = any(sum(reshape(A.', 4, [], size(A, 1)) == 4) > 1, 2);
A(todelete, :) = []

What I do here is:

• A.': transpose A as it is easier to work on column.
• reshape(...): then reshape into rows of 4 elements, each column corresponding to a group of four original columns and the third dimension the original rows of A
• sum(... == 4): sum the number of 4s in each block
• any(... > 1, 2): identify which original row has any block with more than one 4.

[Ammy]

Thank you very much. GOD bless you always.

[Ammy]

How can I exclude those rows in which all the entries are zero?

[Guillaume]

todelete = all(A == 0, 2);

[Ammy]

Sorry it does not work in my case , By taking simple example if I have a matrix like

     0     0     1
     0     0     0
     0     0     2
     0     1     1
     0     2     0

Now in row 2 I have all the zero entries , so I want to exclude this row so that the resulting matrix becomes

     0     0     1
     0     0     2
     0     1     1
     0     2     0

Its a simple example for explanation I have thousands of rows and I want to delete all those rows having all the entries 0.

[Guillaume]

"it does not work"

!! In what way does it not work?

A = [0     0     1
     0     0     0
     0     0     2
     0     1     1
     0     2     0]
todelete = all(A == 0, 2);
A(todelete, :) = []

[Ammy]

Sorry , its work. Thank you for the help.

[Ammy]

A =

     1     2     3     4     0     1     2     3
     0     1     2     3     1     2     3     4
     1     2     3     4     1     1     1     1
     1     2     4     5     3     2     1     2

How can I separate those rows having first four entries are in the order 1 2 3 4 e.g in the above example I want to separate first and third row .

Answer 2

[Jos (10584)]

Here is a flexible example:

% data
X = [4 4] ; % rows starting with this should be discarded
A = [1 4 1 4 ; 4 4 2 2 ; 4 2 4 0 ; 4 4 4 4 ; 2 4 4 2] ; % rows 2 and 4 should be discarded

% engine
tf = ismember(A(:,1:numel(X)), X, 'rows')
A(tf) = [] ; % remove