Remove certain elements from a matrix

I have a text file Pressure which has a lot of rows and two columns and I want to remove the rows and columns where the columns are equal to zero, and display the old graph and new graph on the same plot and this is what i have so far, I don't know what to put in the if statement.

% Copy data from Pressure to OldData
OldData = load('Pressure.txt');

% Copy OldData to NewData
NewData = OldData;

% Remove points where there are zeros
for i = 1:length(OldData)
    if(OldData(i,2) == 0)

      end
  end

% Plot both in same plot:
plot(OldData(:,1),OldData(:,2),'--b',NewData(:,1),NewData(:,2), 'r')

[Azzi Abdelmalek]

Make your Question clear. Avoid details that are not important to resolve your problem. You can post a short example with expected result

Answer 1

[James Tursa]

Replace this:

% Remove points where there are zeros
for i = 1:length(OldData)
    if(OldData(i,2) == 0)

        end
    end

with this:

% Remove points where there are zeros
x = OldData(:,2)==0; % Logical indexes where column 2 is 0
NewData(x,:) = []; % Remove the rows where column 2 is 0

Answer 2

[Roger Stafford]

Or you just write:

   NewData = OldData(OldData(:,2)==0,:);