replace missing values in a matrix

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Richard
Richard on 20 Nov 2012
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?
  1 Comment
Jan
Jan on 20 Nov 2012
Is this matrix a possible input:
A = [1, NaN; ... % NaNs in first row
NaN, 2; ... % Non-NaNs after a NaN
3, NaN]

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Accepted Answer

Jan
Jan on 20 Nov 2012
Edited: Jan on 20 Nov 2012
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
  2 Comments
Image Analyst
Image Analyst on 20 Nov 2012
But you didn't say whether you solved it or not. If you did, mark this as "Answered" otherwise show your code and where you're having difficulty.

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More Answers (1)

Matt J
Matt J on 20 Nov 2012
The FEX has this file
as well as many variants linked to it.

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