"I want to read a .csv file containing numbers with more than 17 decimal digits..."
In fact your file data contains maximum 16 significant digits:
str = fileread('NEOs_asteroids.csv');
raw = regexp(str,'\d*\.?\d+','match');
len = cellfun(@numel,regexprep(raw,'(^0?\.0+|\.)',''));
[mxl,idx] = max(len)
raw{idx}
"How can I keep the same number of decimal digits as in the original file in matlab?"
Whilst importing the file data as text is certainly possible and will retain all of the digits as you request, it will make processing your data afterwards slow and complex. What is much more likely is that you are misunderstand the significance (in the mathematical sense) of those digits and what they represent in DOUBLE values.
Lets take a look at that number:
format long G
num = str2double(raw{idx})
fprintf('%.42f\n',num)
fprintf('%.16g\n',num)
Those values were (most likely) originally saved from DOUBLE values. MATLAB imports those values as the closest DOUBLE values, which perfectly match the DOUBLE values used to create the file. Lets try converting those strings to double and then back again, to see if we lose any information:
vec = str2double(raw);
isequal(vec,str2double(compose("%.16g",vec))) % round-trip conversion
Yep, exactly the same (just as expected). So what you are trying to do is based on a misunderstanding of the significance of DOUBLE values, and will be a lot of effort for absolutely zero benefit.
