How do I delete an entire row if a specific column contains a zero?

Right, so I'm new to MATLAB, but what I have is a large data set (10074x4), the second column of which is a binary code, so whenever theres a zero in that column I want to delete the entire row. Any tips on how to go about doing this? Thanks

Answer 1

[Wayne King]

Many ways in MATLAB. One way:

    %create some data
    X = ones(20,2);
    X(1:10,2) = 0;

    indices = find(X(:,2)==0);
    X(indices,:) = [];

Wayne

[Croy Carlin]

Thanks Wayne, as I'm still getting started with MATLAB, would you mind explaining what each of those steps does? Thanks

[Wayne King]

indices = find(X(:,2)==0);

% find all row indices in the second column of your matrix X that are equal to % zero

X(indices,:) = [];

% get rid of all the rows in X that correspond to the row indices you found

% in the step before

Note that in general find(y==some_value) can be tricky in a computer but in this instance since you are looking for zero, I think you're ok. More about that later.

[Croy Carlin]

Thanks! Now I follow you, thanks again!

[Osama khafajy]

Thanks

Answer 2

[Sean de Wolski]

X = X(logical(X(:,2)),:);

straight conversion to logical will be faster. It is advised to avoid using find and to use logical indexing whenever possible.

Breaking the above into steps, I keep all of rows in which X(:,2) converted to logical (0 = 0,everything else = 1).

[Croy Carlin]

Well that seems tremendously efficient (worked perfectly), could you perhaps run how that works by me one more time? I follow the base logic of converting it then deleting the rows with the zeros, I'm just wondering how that is explained by that code...

[Sean de Wolski]

-taking Wayne's X matrix.

-we convert the second column to a logical vector, i.e. if it's _exactly_ 0 it stays logical (binary) zero (aka false), if it's anything else, it becomes logical one (binary true).

logical(X(:,2))

-Then we extract the rows with a logical one and their corresponding columns in the reassignment to X, the rows with a logical false are tossed.

[Sean de Wolski]

Welcome to MATLAB and Answers!

[Croy Carlin]

Right, I guess I was more wondering if I wanted to do each of those steps individually (convert column to logical, delete 0's, then bring back to "normal" format (not logical)), how would I type those out? (Im just trying to learn all the various ins and outs of MATLAB)

[Sean de Wolski]

X = Waynes_matrix;

index2keep = logical(X(:,2)); %logical second column

X = X(index2keep,:);

Let's say it was something more difficult, e.g. the first column has to equal three and the second column has to be less than pi:

index2keep = X(:,1)==3 & X(:,2) < pi; %first column equal to three and second column less than pi.

X = X(index2keep,:);

[Sean de Wolski]

The best way is just to keep programming. Get a working solution and then ask us/the documentation how to make it better. And of course ask us when you have a specific operation like this, that appears it could be optimized.

[Croy Carlin]

Awesome, that was exactly what I was looking for, cleared a lot up, thanks! No doubt I'll be back for more help as the situation warrants it

[Joshua Goldman]

This worked perfectly for me, too. Thanks very much.

[Aaron Smith]

I know this is a dead thread, but this worked great for me too. It made it so easy to delete any rows in which my first column had a 0. But, how could I do this for a multidimensional matrix? For example, as a single matrix my working code is:

Data = Data(logical(Data(:,1)),:);

but now I need it to do this for 12 other matrices within a for loop. The code I currently have is:

subjects = 12; for sub = 1:subjects

    sheet = ['Sheet' num2str(sub)];

    Data(:,:,sub) = xlsread('801 Matlab Test.xlsx',sheet);

    Data(:,:,sub) = Data(logical(Data(:,1,sub)),:,sub);

end

and I get an error of dimension mismatch. Any ideas?

[Rubina Easmin]

I'm new to MATLAB, I want to delete the entire rows and columns which contain all of ones in a binary image.I want to keep rows and columns if that contain only single zero. Any tips on how to go about doing this? Thanks

>> binaryimage

binaryimage =

33×35 logical array

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1 1 0 0 1

1 1 1 1 1 1 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 1

1 1 1 1 1 1 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0 1

1 1 1 1 1 1 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1

1 1 1 1 1 1 0 0 1 1 1 1 1 1 0 0 0 0 0 0 1 1 0 0 1 1 1 0 0 1

1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 0 0 1

1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 0 0 1

1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 0 0 1

1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 0 0 1

1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 0 0 1

1 1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 0 0 1

1 1 1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 0 0 1

1 1 1 1 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1 1 1 0 0 0 0 1 0 0 1

1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 0 0 1 0 0 1 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 1 0 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

I want to remove rows and columns that contains all of ones