Could someone please tell me what I'm doing wrong.

I'm using a recursive function to remove missing data from a dataset x. But the result that I'm getting is the same as the input matrix even when there is missing data. Whenever there is a missing data in my velocity(2nd column of my matrix), ie.,a NaN, I want to delete those data points from the nearest zero velocity before the missing point to the zero after which a non-zero value occurs.

if true
function r = no_vel_miss( x )      %x is my matrix with all data-time and vel as columns
i=1;
flag=0;
for l=1:length(x(:,1))
  if isnan(x(l,2))                %checking if the value in velocity is NaN
      flag=1;
      break;
  end
end
if flag==0
  r=x;                        %if there is no missing point, return the matrix
else        
while i<=length(x(:,1))         
  if isnan(x(i,2))
      for j=i:-1:1
           if x(j,2)==0
               prezero=j;                %prezero is the nearest zero velocity before missing point
               break;
           end
      end
      for j=i:length(x(:,1))
          if x(j,2)==0&&x(j+1,2)~=0
              postzero=j;                    %postzero is the nearest zero velocity after which a non-zero velocity occurs
              break;
          end
      end
      x_1=cat(1,x(1:prezero,:),x(postzero:length(x(:,1)),:));   %here I'm removing all that data near the missing point as mentioned above
      i=prezero;
      r=no_vel_miss(x_1); 
  else
      i=i+1;
  end 

end
end
end
end

[Jan]

When the posted function does not do what you want, and you do not explain it also, how could we guess how to fix the code? Please edit the question and post the purpose of the code.

A bold guess: If the first column of x contains a NaN, crop all surrounding rows, which contain 0 in the second column. Correct?

Answer 1

[Jan]

Although I do not understand, what the code should do, this looks strange:

i    = 1;
flag = 0;
for l = 1:length(x(:,1))
  if isnan(x(i,2))
    flag = 1;
    break;
  end
end

This is a loop over "l" (lowercase L), but the body of the loop depends on "i". Is this a typo?

What about omitting the loop and using:

flag = any(isnan(x(:, 2)));

[Nagesh A P]

Thanks. That was a typo. Also, do recursive functions take so much time to execute?

[Jan]

Yes, calling the function recursively consumes a lot of memory, because you duplicate large parts of the input array in each call. But this is not useful here at all. A simpler non-recursive version:

function r = no_vel_miss(x)
keep = true(size(x, 1));
miss = find(isnan(x(:, 2))).';
x0   = find(x(:, 2) == 0);
for k = miss
   index = find(k > x0, 1);
   keep(x0(index)+1:x0(index + 1)-1) = false;
end
r = x(keep, :);
end

I'm not sure if this does exactly, what you want. But it should clarify how to simplify your code.