TEXTSCAN is my personal nemesis: Quotes strings with commas
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Dear all,
I thought I acquired some Matlab knowledge over the years. But textscan really makes me feel dumb. I can not figure out the syntax to read a quoted text file.
Let's say I have a text file with the following format:
"L1: quoted text, with commas","111.111",123\n
"L2: quoted text, with commas","222.222",234\n
...
(the field width are the same just for the example; consider them variable in the real world).
Now my understanding of textscan's formatSpec would be:
format = '%q,"%f",%f';
delim = '\n';
res = textscan(fileId,format,'Delimiter',delim,'ReturnOnError',false);
This is because I am assuming that %q considers everything between two quotes as part of the same string, as the help states
"If the string begins with a double quotation mark ("), omit the leading quotation mark
and its accompanying closing mark, which is the second instance of a lone double
quotation mark"
However this fails with the ominous error message:
Error using textscan
Mismatch between file and format string.
Trouble reading 'Literal' field from file (row number 1, field number 2) ==>
"L2: quoted text, with commas","222.222",234\n
So the commas in the quoted string somehow screw-up the parsing, since using the regexp-like
format = '"%[^"]","%f",%f';
instead of %q works perfectly fine.
So my questions are:
- What am I doing wrong?
- Why is there the %q option if it does not treat everything in between as string (as this would than simply be a shorthand for "%s")?
- Am I using the delimiter option correctly?
Any help appreciated!
Greetings, David
2 Comments
Accepted Answer
Stephen23
on 13 Feb 2017
Edited: Stephen23
on 13 Feb 2017
fmt = '%q"%f"%f';
fid = fopen('temp5.txt','rt');
C = textscan(fid,fmt,'Delimiter',',');
fclose(fid);
Gives this:
>> C{:}
ans =
'L1: quoted text, with commas'
'L2: quoted text, with commas'
ans =
111.1110
222.2220
ans =
123
234
And your questions:
- you are over-specifying the delimiter, and also confusing the delimiter with the end of line character |
6 Comments
Stephen23
on 13 Feb 2017
Edited: Stephen23
on 13 Feb 2017
@David J. Mack: the task is complicated by having numeric fields surrounded by double quotes, which is rather erroneous because double quotes always indicate strings. Two solution for this are:
- Change the file writing so that it correctly does not put double quotes around numeric values.
- Import the numeric values are strings using %q, and quickly convert them using str2double once inside MATLAB.
In both of these cases you could go back to defining the delimiter as just the comma, which would avoid collapsing fields together.
More Answers (2)
Jeremy Hughes
on 16 Feb 2017
If you have access to R2016b, try using detectImportOptions with readtable.
opts = detectImportOptions(yourfile);
T = readtable(yourfile,opts)
I think this will do what you want without a lot of fuss.
David J. Mack
on 13 Feb 2017
Edited: David J. Mack
on 13 Feb 2017
1 Comment
Serge
on 27 May 2018
Any suggestions for this question:
https://au.mathworks.com/matlabcentral/answers/402792-yet-another-textscan-question
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