replace missing values in a matrix

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Richard
Richard il 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 Commento
Jan
Jan il 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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Risposta accettata

Jan
Jan il 20 Nov 2012
Modificato: Jan il 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 Commenti
Richard
Richard il 20 Nov 2012
not homework, just needed some advice...
Image Analyst
Image Analyst il 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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Più risposte (1)

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

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