Question

Could anyone help how should I use the interp1-function on MATLAB on data such as the following:

   -99
     3
     1
     7
    10
    10
    22
    29
   -99
   -99
    25
    26
    60
   142
    78
   124
    74
    26
    13
    18

The -99 data values correspond to error-values and I would like to interpolate them…advices? =) Thank you!

Answer 1

Not around Matlab at the moment but I reckon you could do something like this:

    Y =  [-99
         3
         1
         7
        10
        10
        22
        29
       -99
       -99
        25
        26
        60
       142
        78
       124
        74
        26
        13
        18];

%Make an array of x values - I'm assuming yours are evenly spaced
Xi = 1:length(Y);

%remove the -99 points
errors = Y == -99;
X = Xi(~errors);
Y = Y(~errors);

Yi = interp1(X, Y, Xi);

So in the code X and Y are the x and y coord vectors of the points you want to interpolate, i.e. your input points (without the errors!), and Xi is a vector of the location of the points you would like to interpolate values for (if you think about X being location and Y being value). The point Yi will be the interpolated values corresponding to Xi, which I think in this case will be your original vector with the -99 points replaced by linearly interpolated values. Funny stuff might happen at the edges :/ check the docs. Hope there are no errors.