If you want to replace only the duplicates with 'NaN' and keep one occurrence of each value intact, here is the code:
% Sample array (Replace this with your 40,000x3 array)
array = [
2.3930, 0, 6.1680;
2.3872, 0, 6.1680;
2.3848, 0, 6.1780;
2.3738, 0, 6.1680;
2.3741, 0, 6.1690;
2.3702, 0, 6.1780;
2.3688, 0, 6.1690;
2.3635, 0, 6.1780;
];
% Extract the third column
third_col = array(:, 3);
% Find unique values and their first occurrence index
[unique_vals, ~, ic] = unique(third_col);
% Count the occurrence of each unique value
counts = accumarray(ic, 1);
% Identify values that occur more than once (duplicates)
duplicate_vals = unique_vals(counts > 1);
% Replace only duplicates with NaN, keep one occurrence of each value
for val = duplicate_vals'
idx = find(third_col == val);
third_col(idx(2:end)) = NaN; % Keep the first occurrence, replace the rest with NaN
end
% Update the third column in the original array
array(:, 3) = third_col;
% Display the updated array
disp(array);
In this code, for each duplicate value, find its indices in the third column using 'find'. Then, keep the first occurrence (index idx(1)) and replace the rest (idx(2:end)) with NaN. This will leave one instance of each value in the third column and replace only the duplicates with 'NaN'.
