Read values from a very complex txt file into matlab

Question

Pedro Cavaco 2011-4-6

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https://ww2.mathworks.cn/matlabcentral/answers/4912-read-values-from-a-very-complex-txt-file-into-matlab

Dear Matlab community,

I have a data file of wave heights that looks like this:

 Euro platform;Golfhoogte, significante-, uit energiespectrum van  30-500 mHz in cm;1982-11-19;19:00;;361;cm;NVT;Tijdreeks en frequentie analyse, methode CIC/MAREG;Nationaal;Stappenbaak - type Marine 300;NVT;NVT;4230;51.9986111;3.2763889;NVT;NVT,NVT,Niet van toepassing
Euro platform;Golfhoogte, significante-, uit energiespectrum van 30-500 mHz in cm;1982-11-19;22:00;;363;cm;NVT;Tijdreeks en frequentie analyse, methode CIC/MAREG;Nationaal;Stappenbaak - type Marine 300;NVT;NVT;4230;51.9986111;3.2763889;NVT;NVT,NVT,Niet van toepassing
Euro platform;Golfhoogte, significante-, uit energiespectrum van 30-500 mHz in cm;1982-11-20;01:00;;379;cm;NVT;Tijdreeks en frequentie analyse, methode CIC/MAREG;Nationaal;Stappenbaak - type Marine 300;NVT;NVT;4230;51.9986111;3.2763889;NVT;NVT,NVT,Niet van toepassing
Euro platform;Golfhoogte, significante-, uit energiespectrum van 30-500 mHz in cm;1982-11-20;04:00;;381;cm;NVT;Tijdreeks en frequentie analyse, methode CIC/MAREG;Nationaal;Stappenbaak - type Marine 300;NVT;NVT;4230;51.9986111;3.2763889;NVT;NVT,NVT,Niet van toepassing

I am only interested in reading the date (column 3) the hour (column 4) and the wave height, (column 6). The file has 18 columns and is Semicolon(;) separated, so the commas in between the strings can be ignored. There is an empty column among the hour and wave height, that's why wave height is in column 6 and not 5. The length of the file is very big, something like (28years * 365days * 24 h*60 min) in length.

I am using the command:

[data(:,1),data(:,2)...data(:,18)] = textread('wave.txt','%q %q %q %q %q %q %q %q %q %q %q %q %q %q %q %q %q %q','delimiter',';');

This method works but is very very slow, and it gave me some problems with 'buffersize' memory sometimes. Do you guys know a better way to do this? Maybe read only the date and wave heights and dump all the crappy text?

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Answer 1

Laura Proctor 2011-4-6

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在 MATLAB Online 中打开

You can ignore data in textread using the asterisk (*) after the percentage symbol when reading in data.

For example, if you have 4 columns and only wish to read in the first and third columns of data:

data = textread('myFile.txt','%s %*f %f %*f','delimiter',';');

Also, you may wish to look at the documentation for TEXTREAD to see if you can read in the data using better formats other than %q which is used to read in a double quoted string. It seems that you have some numeric data that would be well suited for %f.