How do I parse and erase from a string while importing CSV with tableread?
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Daniel Bridges
on 23 Jan 2018
Commented: Peter Perkins
on 25 Jan 2018
I have found extractBefore, but how do I succinctly apply it to each opts.VariableNames element? Should I use cellfun? I will try it instead of a for loop, but I don't see how to use cellfun for a function requiring an input argument (namely, '_').
Why does MATLAB not allow for the following 'intuitive' syntax?
>> opts.VariableNames(:) = extractBefore(opts.VariableNames(:),'_')
Error using matlab.io.ImportOptions/set.VariableNames (line 185)
Expected a cell array of valid variable names.
>> opts.VariableNames = extractBefore(opts.VariableNames,'_')
Error using matlab.io.ImportOptions/set.VariableNames (line 185)
Expected a cell array of valid variable names.
The following code is what I am seeking to improve with this task, by automatically truncating the latter column names.
filepath = 'easy.csv';
opts = detectImportOptions(filepath, 'NumHeaderLines', 1);
opts = setvartype(opts,opts.VariableNames, 'double');
opts.VariableNames(1)={'Dose'};
DVH = readtable(filepath,opts)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/169334/image.png)
1 Comment
Guillaume
on 23 Jan 2018
Why does MATLAB not allow for the following 'intuitive' syntax?
>> opts.VariableNames(:) = extractBefore(opts.VariableNames(:),'_')
Because
extractBefore(opts.VariableNames{1},'_')
returns an empty char array (since VariableNames{1} doesn't have a _) which is not a valid variable name.
opts.VariableNames(2:end) = extractBefore(opts.VariableNames(2:end),'_')
would have worked.
By the way, note that the (:) in VariableNames(:) was pointless in your original code. The only thing that it did is transpose the cell array from a row vector to a column vector.
Accepted Answer
Daniel Bridges
on 23 Jan 2018
Edited: Daniel Bridges
on 25 Jan 2018
3 Comments
Guillaume
on 23 Jan 2018
Well as Walter says, the StripExtraStuff function with just one line is a bit pointless. Since you've added a _ to the first variable name, you could just have
opts.VariableNames{1} = 'Dose_';
opts.VariableNames = extractBefore(opts.VariableNames, '_');
If you use regexprep, then you don't need the extra _ for the first variable.
opts.VariableNames{1} = 'Dose';
opts.VariableNames = regexprep(opts.VariableNames, '_.*', ''); %replace _ followed by any number of any characters by empty
Both methods are just as efficient.
More Answers (1)
Peter Perkins
on 24 Jan 2018
Fixing the names in the importOptions setting is one choice, but an alternative might have been to patch up the names after reading the file with readtable (you'd still have to skip the header line). Perhaps something like
DVH.Properties.VariableNames{1} = 'Dose'; DVH.Properties.VariableNames(2:end) = extractBefore(DVH.Properties.VariableNames(2:end), '_')
3 Comments
Guillaume
on 25 Jan 2018
If you were just using detectImportOptions so as to be able to override the variable names then changing them after the fact and not bothering with the import options may be simpler (*)
Since you've got to do the import options to override the type then you may has well override the names.
(*) Except that, frustratingly, in some cases, readtable without import options and readtable with default import options will read the table differently.
Peter Perkins
on 25 Jan 2018
Daniel, I'm usually an advocate of fixing things at their source. My suggestion was more about simplicity. But as Guillaume says, if you're using detectimportoptions anyway ...
Guillaume, I hear you about frustrating, but it's a tension between backwards compatibility, and better new behavior. We try to walk a fine line between providing better behavior by default, and not breaking code that relied on the older behavior.
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