MATLAB: Replace missing values in a matrix

matrixnan

Consider the following:
A = [1,1,1;
    2,3,1;
    nan,3,1;
    nan,3,nan];
how would I replace the missing values with the previous values? For example:
data =
       1     1     1
       2     3     1
       2     3     1
       2     3     1
I can find the nan by isnan(data) but I don't know how to replace the values as described.
Amended:
I've managed to do this but not in a very concise way:
A = [1,1,1;2,3,1;nan,3,1;nan,3,nan];
B = ~isnan(A);
I = arrayfun(@(x)find(B(:,x),1,'last'),1:size(A,2));
for i = 1:size(A,2);    
    C = A(:,i);
    D = isnan(C);
    C(D) = C(I(i));
    Final(:,i) = C;
end
Could anyone suggest on a way to tidy this up?

Best Answer

What about a simple loop:
  • Go through the rows from 2 to end
  • Use isnan() to find the indices of NaNs
  • Replace values in the current row by the ones of the former row.
I'm not more specific, because this could be a homework also.
[EDITED]
for k = 2:size(A, 1)
  index       = isnan(A(k, :));
  A(k, index) = A(k - 1, index);
end
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