How do I shift columns (left or right) in a matrix

Hi All,

I would like to non-circularly shift my matrix and then have zeros padded to either the left or right (depending on the shift) i.e. if the matrix shifts to the right, zeros would be padded to the left.

My code so far looks like this:

%dummy data
data = rand(5, 16);

channelSink = 9; %this variable will either be >layerIV, <layerIV or =layerIV
layerIV = 7;
chDiff = layerIV - channelSink;

    
    for channel = 1:16
    
        if channelSink > layerIV 
            
            %shift columns to the left by ab(chDiff)
            %and
            %set columns shifted by ab(chDiff) to zero
            
        elseif channelSink < layerIV
            
            %shift columns to the right by chDiff
            %and
            %set columns shifted by chDiff to zero
            
        else %if chDiff = 0, don't shift
              
              chDiff = 0; 
              disp('Sink at channel 7; not necessary to re-align');
             
        end
        
    end
      

Thank you in advance.

Answer 1

[Walter Roberson]

shift = abs(diff)
%left
data = [data(:, shift+1:end), zeros(size(data,1),shift)]
%right
data = [zeros(size(data,1),shift), data(:, end-shift:shift)];

Note: we recommend against using diff() as a variable name, as it conflicts with the common function diff() . If nothing else, it will tend to confuse other people who read your code.

[NA]

The matrix shifts to the left perfectly, however, when I apply the code to shift the matrix to the right, only zeros padded to the left appear, without the shifted data.

Thank you, I shall refrain from using diff() as a variable name in future context, and will update my code above.

[Walter Roberson]

%right
data = [zeros(size(data,1),shift), data(:, shift:end-shift)];

[NA]

Thank you, Walter. I just made a tiny adjustment as the shifted columns were off by 1.

data = [zeros(size(data,1),shift), data(:, shift-1:end-shift)];

But, it works perfectly now. Thanks again!

Answer 2

[Abdolkarim Mohammadi]

I used the vectorization capability of MATLAB, so it is faster and there is no need for a for loop.

data = rand (5,16);
channelSink = 9; % this variable will either be >layerIV, <layerIV or =layerIV
layerIV = 7;
diff = layerIV - channelSink;

dataFirstCol = 1;
dataLastCol = size (data,2);

dataShiftedFirstCol = 1;
dataShiftedLastCol = size (data,2);

if diff < 0
	dataFirstCol = dataFirstCol + abs(diff);
	dataShiftedLastCol = dataShiftedLastCol - abs(diff);
elseif diff > 0
	dataLastCol  = dataLastCol  - abs(diff);
	dataShiftedFirstCol = dataShiftedFirstCol + abs(diff);
end

dataShifted = zeros (size(data));
dataShifted (:,dataShiftedFirstCol:dataShiftedLastCol) = data (:,dataFirstCol:dataLastCol);

[NA]

Thanks for this. The reason I wrote my code in a for loop was because I need to run it on multiple datasets (n x 16 matrix). But I will try and adapt what you have done to suit what I want. I do apprecaite your help.

Answer 3

[Bruno Luong]

k > 0 shift right

k < 0 shift left

A*diag(ones(1,size(A,2)-abs(k)),k)