Interpolating missing values
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Jenny
il 3 Nov 2011
Risposto: Jennifer Rebbin
il 20 Set 2023
I have a matrix with NaNs in some of the cells. I need to find all cells of the matrix with NaN values, then interpolate the missing values using the first value before and after the NaNs, and put the interpolated values in the place of the NaN values within the matrix. NaNs may be only one at a time or several in a row, the first and last value around NaN sections may span more than one row.
I have looked at find and interp1 in Matlab help, but can't make it work for my situation. For example: how do you make find locate NaN values? And with interp1, I am not sure what all the variables should be in this case. Any tips?
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Fangjun Jiang
il 3 Nov 2011
Interpolation on a 1-D vector is not that hard. Maybe it could be expanded to 2-D matrix too. See if interp1() is all you need.
%%original data
x=1:0.1:10;
y=sin(x);
ind=round(ceil(90*rand(10,1)));
y(ind)=nan;
figure(1);plot(x,y);
%processing
ind=~isnan(y);
NewY=interp1(x(ind),y(ind),x);
figure(2);plot(x,NewY);
For 2-D
%%original good data
[x,y,z]=peaks;
figure(1); surf(x,y,z);
%missing some z values
[m,n]=size(z);
ind_m=ceil((m-1)*rand(10,1));
ind_n=ceil((n-1)*rand(10,1));
Incomplete_z=z;
Incomplete_z(ind_m,ind_n)=nan;
figure(2);surf(x,y,Incomplete_z);
%interpolate to recover z
index=isnan(Incomplete_z);
row_index=any(index,2);
col_index=any(index,1);
NewX=x(~row_index,~col_index);
NewY=y(~row_index,~col_index);
NewZ=Incomplete_z(~row_index,~col_index);
Interpolate_z=interp2(NewX,NewY,NewZ,x,y);
figure(3);surf(x,y,Interpolate_z)
2 Commenti
Fangjun Jiang
il 6 Nov 2011
2-D is similar. You need to get rid of the rows and columns where any element in the row or column is nan. See update.
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