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From: John D'Errico on 18 Jun 2010 05:15
"Stephanie " <stephanie.turnbull(a)strath.ac.uk> wrote in message <hut2io$mf8$1(a)fred.mathworks.com>...
> Hi there,
>
> I have a vector where the first few values at the beginning and end are NaN, and I would like to replace these values with the nearest "real" value.
>
> For example;
>
> NaN
> NaN
> NaN
> 3
> 6
> 10
> 30
> 100
> NaN
> NaN
>
> Would become;
>
> 3
> 3
> 3
> 3
> 6
> 10
> 30
> 100
> 100
> 100
>
> Also, could this be applied to a matrix with the same problem? E.g. the first few rows and the last few rows of a matrix all contain NaN to be filled with nearest non-NaN value?
>
> Many thanks,
> Steph

I'm surprised nobody responded to this when it
was posted. Perhaps the issue is it is trivial to
solve for a vector, but not so in two dimensions.

Thus for a vector, you would simply find the first
non-NaN element, and replace everything before it
with that number. Do the same with the last non-NaN
element.

That rule fails for an array however. Or what if you
have NaNs inside the vector? Again, this becomes
more difficult. Will you try to interpolate then?

A scheme that will do reasonably well, with a smooth
interpolant in one or two dimensions is inpaint_nans,
using its method 4. Its a bit overkill, but it works.

X0 = [nan; nan; nan; 3; 6; 10; 30; 100; nan; nan];
X1 = inpaint_nans(X0,4);
[X0,X1]
ans =
NaN 3
NaN 3
NaN 3
3 3
6 6
10 10
30 30
100 100
NaN 100
NaN 100

Find inpaint_nans on the file exchange.

http://www.mathworks.com/matlabcentral/fileexchange/4551

HTH,
John
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