I need to replace an enitre row, if any of the value goes less than zero

I need to check each row, whether is there any of the value less than zero in a particular row. If any value in a row is less than zero, i have to replace the entire row itself.

For example,

a1=[1 2; 3 4; -5 6] a2=[22 23; 56 78; 89 75]

Step 1: I need to check whether any element of a row is less than zero in matrix a1...... Step 2: If there is any negative value, i have to replace that particular row by the the same row of the another matrix a2.

Problem with the coding I did, If there is only one negative value in a row, then the negative value only is replaced by the another matrix of the same (row,column), but I couldn't replace the entire row.

Answer 1

[Hikaru]

This will solve it.

    a1=[1 2; 3 4; -5 6]
    a2=[22 23; 56 78; 89 75]

    neg = a1<0 % return '1' for values less than zero
    a1(neg,:) = a2(neg,:) % step 2

[Suman]

Thank you :-)

[Suman]

I am getting this error.

Index exceeds matrix dimensions.

Error in Test_2_20feb15 (line 82) X(Negative,:) = X_previous(Negative,:);

[Stephen23]

Are both of X and X_previous really the same size? Use the size command and tell us exactly what their sizes are.

This error arises because negative is referring to positions in one of the matrices that do not exist. Because negative is calculated from X, it is likely that X_previous is smaller than X, thus giving this error.

[Hikaru]

Now that I redo this problem with another matrix, the solution above does not work if the negative value is located in the second column.

Assuming you have matrix of 2 columns only, you might want to try the code below:

    neg1 = a1(:,1)<0
    neg2 = a1(:,2)<0
    neg = neg1|neg2
    a1(neg,:) = a2(neg,:)

I haven't fully tested it, but it should give you a start. Like Stephen said, you need to be more specific for a more specific solution.