CODEWITHSUNDEEP
matlabreplacenan
phdstudent
phdstudent

Reputation: 1144

Replace NaN with last non-NaN value

I have a matrix with several NaN values and I want to replace those with the last non-NaN value. The matrix is very large so ideally I would do it in a vectorized fashion.

Here is a minimal working example:

M = [
NaN NaN NaN 3
7   NaN NaN 1
NaN NaN NaN 9
NaN 6   NaN NaN
NaN NaN NaN NaN
8   NaN NaN 8
NaN 5   NaN NaN
NaN NaN NaN NaN
9   NaN NaN NaN]

And the output should be:

Out = [
NaN NaN NaN 3
7   NaN NaN 1
7   NaN NaN 9
7   6   NaN 9
7   6   NaN 9
8   6   NaN 8
8   5   NaN 8
8   5   NaN 8
9   5   NaN 8]

I was wondering whether anyone faced a similar problem and knows an efficient way to solve it. I have read this similar post but all solutions seem to involve a for loop.

Upvotes: 1

Views: 390

Answers (2)

CKT
CKT

Reputation: 781

Check out the fillmissing function if you have R2016b or beyond. You can use the 'previous' method to do exactly this.

Upvotes: 3

Divakar
Divakar

Reputation: 221564

Here's one vectorized approach -

mask = ~isnan(M);
cumsums = cumsum(mask,1);
invalid_mask = cumsums==0;
cumsums(invalid_mask) = 1;

shifts = [0 cumsum(sum(mask(:,1:end-1),1))];

idx = bsxfun(@plus,cumsums, shifts);
nums = M(mask);
out = nums(idx);
out(invalid_mask)=nan;

Upvotes: 6

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