Interpolate

Hi,

I could use some help with a script that I am writing. I have one excel file with 4100 rows and 225 columns consisting of numbers. In case of one or multiple zeros, I want to interpolate these values with the neighbouring numbers. What I did:

function data = interp_datatest(data, method)

orig_valid = find(data(:,:)); %to interpolate all columns and rows 

% to test not-0 values
valid_test = orig_valid(1 : end-1); %I cannot use the first and the last datapoint because there are no neighbouring numbers

% to interpolate indices
calc = valid_test(data (valid_test,:)== 0);

% which values are valid?
% first I make a logical array with only zeros
valid = zeros(length(data),1); 

% make the not 0-values 1 
valid(orig_valid) = 1; % everything with the number '1' is valid and not a zero.

valid(calc) = 0;
valid = logical(valid);
calc = ~valid; % invert valid values for the to be interpolated %values

% interpolate with methode 'spline' 
data(calc,:) = interp1(data(valid,1), data(valid,:), data(calc,1), method);

%Loop for all the columns
[rows,columns] = size(data);
for idx = 1:columns

end

There are mistakes in the script. Please help me find them. Another thing I would like to add but I don't know how is that if there are more than 5 consecutive zeros, I do not want to interpolate and leave the zeros.

Thanks a lot for your comments! M

Answer 1

[Teja Muppirala]

Here's one possible way to do it. I've handled the 5 consecutive zeros thing by using IMCLOSE, a function from the Image Processing Toolbox if you have it.

% This is used to find regions with >= 5 consective zeros
mask = imclose(data,[1;1;1;1;1]);

for col = 1:size(data,2);
    %Find the locations and values of nonzero data
    [valid,~,values] = find(data(:,col));

      %Do not use zeros at the end or the beginning
      valid_zeros = intersect(valid(1):valid(end),find(~data(:,col)));

      %Call interp1
      data(valid_zeros,col) = interp1(valid,values,valid_zeros,method);
  end;
  data = data.*mask;

Answer 2

[Mariska Kret]

Thnx for the reply. When I run your script, I get the following errror:

??? Error: File: interpolate_excelfile.m Line: 6 Column: 13 Expression or statement is incorrect--possibly unbalanced (, {, or [.

M

[Teja Muppirala]

You get that error when there are parentheses that are not closed, like:

(5*(2+3)

I don't see that in the script above. You should check line 6 of your file for that sort of error.

[Walter Roberson]

Mariska, try replacing the ~ on line 6 with an otherwise unused variable name, e.g.,

[valid,unused,values] = find(data(:,col))

[Teja Muppirala]

Ah. Good call! Sometimes you take these things for granted...