Import data file with comma decimal point

Question

J. 2012-12-23

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https://ww2.mathworks.cn/matlabcentral/answers/57276-import-data-file-with-comma-decimal-point

评论： Jon 2022-9-26

Hi !

I have a problem with importing a data file, and I hope someone in here can help resolve it. The file I'm trying to import looks like this (headers not included!):

01-11-2012 00:00:00  52,0837766666504  -2752,54346603125  0  -4280  1  1  2  2  0  0
01-11-2012 00:00:10  55,0510711669922  -2052,33987375  0  -9240  1  1  2  2  0  0
01-11-2012 00:00:20  58,0332733895508  -2952,54345703125  0  -3240  1  1  2  2  0  0

A total of 11 columns separated by tab, stored in a .txt file.

The problem is:

1st column has date and time, which Matlab seems to have troubles with
2nd and 3rd uses comma decimal instead of a dot, which makes Matlab see it as text

I've tried to load the file with the function "load" - which isn't possible because of the mix of data and text. Then I tried using "textscan" which results in an array inside an array, with completely messed up data (all headers in a 1x1 array fx).

Using the following code:

filename = 'test.txt';
delimiterIn = ' ';
headerlinesIn = 1;
A = importdata(filename,delimiterIn,headerlinesIn);

Produced a 1x1 array with all the headers and nothing else (I also tried /t for the delimiter, which didn't work at all).

So this is the point where I hope someone in here can help :) Thanks in advance, and a Merry Christmas to you all! :)

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Answer 1

Azzi Abdelmalek 2012-12-23

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https://ww2.mathworks.cn/matlabcentral/answers/57276-import-data-file-with-comma-decimal-point#answer_69282

编辑：Azzi Abdelmalek 2012-12-23

在 MATLAB Online 中打开

fid = fopen('file.txt');
out=textscan(fid,'%s  %s  %s  %s   %s  %s  %s  %s %s  %s  %s  %s ')
fclose(fid);

Then you can arrange your data

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Azzi Abdelmalek 2012-12-23

You have just to concatenate them

Azzi Abdelmalek 2012-12-23

在 MATLAB Online 中打开

a=out{1};b=out{2};
for k=1:numel(a)
  dat{k}=datenum(strcat(a(k,:), b(k,:)))
end

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Answer 2

per isakson 2012-12-23

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编辑：per isakson 2020-8-4

在 MATLAB Online 中打开

This functions replaces all "," by ".". Make a copy of your file first. Import in next step.

    function    comma2point_overwrite( filespec )
    % replaces all occurences of comma (",") with point (".") in a text-file.
    % Note that the file is overwritten, which is the price for high speed.
        file    = memmapfile( filespec, 'writable', true );
        comma   = uint8(',');
        point   = uint8('.');
        file.Data( transpose( file.Data==comma) ) = point;
        %%%delete(file)
    end

Not sure whether it works with unicode:(

.

Correction:

The statement

delete(file)

is in error. Remove it. memmapfile is a value class and has no delete method. Now it works here (R2012a,Win7). Demo:

    >> comma2point_demo
    M =
      123.4000  567.8000
      123.4000  567.8000
      123.4000  567.8000
    >>

where

    %%comma2point_demo
    copyfile( 'cssm.txt', 'comma2point.txt' )
    comma2point_overwrite( 'comma2point.txt' )
    M = dlmread('comma2point.txt')

and cssm.txt contains

    123,4 567,8
    123,4 567,8
    123,4 567,8

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Mustafa Calcuttawala 2020-5-22

编辑：Mustafa Calcuttawala 2020-5-22

在 MATLAB Online 中打开

@per isakson You the real mvp my man. Your code is a charm. However, when you try and open the file in excel while the memmapfile is still defined and present in the workspace, excel shows an error that the file can't be edited and forces you to open the file as read only. This is probably because the memmapfile has not been removed from the workspace. The statement

delete(file)

doesn't help removing the file. This is the error that comes up:

Error using delete

Name must be a string scalar or character vector.

To remove the memmapfile variable, simply use the command

clearvars file

And problem solved.

per isakson 2020-5-23

编辑：per isakson 2020-5-23

Thanks for your comment, however I don't fully understand your description.

"[...] while the memmapfile [object] is still defined and present in the workspace" Which workspace do you refer to?

The data file is obviously locked for writing as long as an memmapfile object of that data file exists. (I fail to find a page in the documentation to link to.) Thus, when comma2point_overwrite() is running one cannot open the data file for writing in another program, e.g. Excel. The lifecycle of the memmapfile object ends when comma2point_overwrite() ends and at this point in time the data file is released.

Your description makes me think that you have copied the body of the function comma2point_overwrite() to a script. In that case clearvars is needed to destroy the memmapfile object and thereby release the data file.

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Answer 3

Walter Roberson 2020-8-4

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In fairly recent versions of MATLAB, readtable() can now process text files that use comma as decimal point. If it does not automatically detect the comma, then use the option 'decimal', 'comma'