MATLAB: Check a date in a formatted text file for a match, regexp help

datefile readingformatspecregexptext file

In the attached file there are some Categories for some dates (positively disturbed, negatively disturbed, quiet). I am trying to write a program that takes a date e.g. '12-Mar-2010' and checks from this file what category that date belongs to. (Or if it is not in any of the three categories). I'm stuck with file reading due to the strange format of this file. I have tried textscan, fileread, regexp with different formatspecs but am unable to get all this data into some easily to process form (matrices may be) for easy comparison with given date/dates. Any help is appreciated.

Best Answer

A fairly straightforward method:

%read whole file in one go
fid = fopen('q_d_daysctl.txt', 'rt');  %using 't' to autoconvert \r\n into \n. Unfortunately fileread does not do that
filecontent = fread(fid, '*char')';
fclose(fid);
%parse file using regexp. Because of the lineanchor option, requires \n as EOL, not \r\n.
%regex has eight tokens
%1: optional, text, space and ':' to match the line heading (positively disturbed, etc.)
%2 - 6: match number or '.' and the following spaces
%3: match month (the '.' is not part of the token but part of the match)
%4: optional, match 4 digit year and preceding space
rows = regexp(filecontent, '^([A-Za-z: ]+)?(\d+|\.) +(\d+|\.) +(\d+|\.) +(\d+|\.) +(\d+|\.) +([A-Z][a-z]{2})\.( \d{4})?$', 'tokens', 'lineanchors');
rows = vertcat(rows{:});  %convert into nx8 cell array
%fill holes, convert numbers, then convert to table
rows(:, 1) = fillmissing(strtrim(rows(:, 1)), 'previous');
rows(:, 2:6) = num2cell(str2double(rows(:, 2:6)));
rows(:, 8) = num2cell(fillmissing(str2double(rows(:, 8)), 'previous'));
datecat = cell2table(rows, 'VariableNames', [{'category'}, compose('day%d', 1:5), {'month', 'year'}])
%unstack the whole lot for easy search
datecat = stack(datecat, 2:6, 'NewDataVariableName', 'day', 'IndexVariableName', 'ignore')
datecat(isnan(datecat.day), :) = [];  %get rid of days that were '.' in the original file

For good measure, I'd convert the month, year, day columns into a single datetime column and the category column into a categorical, but the datecat table is easily searchable as it is.

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MATLAB: Using regexp to Search Large Text File for Wanted Data

is regexp the best method?

For EL HGT, probably. For your Northing/Easting for UTM(Zone 15), no because extracting that value involve crossreferencing rows and columns. For that you would have to parse the whole file, and you would have to write your own parser as none of matlab built-in parsers (textscan, etc.) can parse a file that complex as is.

However, if UTM(Zone 15) is always the first column of number for Northing/Easting, then yes you could use a regexp:

filecontent = fileread('sample.txt');
el_hgt_full = regexp(filecontent, '(?<=EL HGT:\s*)[^\n\r]*', 'match', 'once');
el_hgt = str2double(regexp(el_hgt_full, '[+-]?\d+(\.\d+)?', 'match'));
northing = str2double(regexp(filecontent, '(?<=Northing \(Y\) \[meters\]\s*)[+-]?\d+(\.\d+)?', 'match', 'once'));
easting = str2double(regexp(filecontent, '(?<=Easting \(X\)  \[meters\]\s*)[+-]?\d+(\.\d+)?', 'match', 'once'));

MATLAB: How to extract rows from a text file with a specific start

% Parameter:
FileName = 'C:\Your data file.txt';
Key      = '$GNGGA';
NewFile  = 'C:\Fixed.txt';
% Import text file and select lines starting with the Key string:
Str   = fileread(FileName);
CStr  = strsplit(Str, '\n');
Match = strncmp(CStr, Key, length(Key));
CStr  = CStr(Match);
% Create new file and write matching lines:
fid = fopen(NewFile, 'w');
if fid == -1
  error('Cannot create new file: %s', NewFile);
end
fprintf(fid, '%s\n', CStr{:});
fclose(fid);

Best Answer

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MATLAB: Using regexp to Search Large Text File for Wanted Data

MATLAB: How to extract rows from a text file with a specific start

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