How can I read csv file data correctly? I tried multiple ways

Question

Nora Khaled 2020-11-2

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评论： Mathieu NOE 2020-11-3

Hi

I have a csv file and I am trying to import it to matlab. an example for the file content is the following (this is one row)

689d-40bf-9c61-551c0c1a69bf,true,"timestamp"," 2"," 8"," 2",25.21,17.536593101926,39,62

I tried using

readtable()

but the file is not separated as it is by the commas.

Then, I tried

csvread()

and I get the error:

Error using dlmread (line 147)
Mismatch between file and format character vector.
Trouble reading 'Numeric' field from file (row number 1, field number 1) ==>

Also, I tried

textscan()

and it did not do anything(no error but no content extracted either)

Last thing, I tried to manually import the data using the interface but the same problem in the readtable() occurred.

How can I read the data correctly? and put it in a matrix or table

Thank you

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Answer 1

Stephen23 2020-11-2

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编辑：Stephen23 2020-11-2

在 MATLAB Online 中打开

temp0.txt

textscan has no problems importing the file data simply and efficiently (sample file is attached):

opt = {'Delimiter',',','CollectOutput',true};
fmt = '%s%s%q%q%q%q%f%f%f%f';
[fid,msg] = fopen('temp0.txt','rt');
assert(fid>=3,msg)
out = textscan(fid,fmt,opt{:});
fclose(fid);

Giving:

>> out{1} % character data
ans = 
    [1x27 char]    'true'    'timestamp'    '  2'    '  8'    '  2'
    [1x27 char]    'true'    'timestamp'    '  3'    '  9'    '  1'
    [1x27 char]    'true'    'timestamp'    '  4'    ' 10'    '  0'
    [1x27 char]    'true'    'timestamp'    '  5'    ' 11'    ' -1'
>> out{2} % numeric data
ans =
   25.2100   17.5366   39.0000   62.0000
   25.2300   17.5366   40.0000   63.0000
   25.2400   17.5366   41.0000   64.0000
   25.2500   17.5366   42.0000   65.0000
>>

Because readtable also supports the format specifier I see no reason why it shouldn't work as well. I might try later.

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Nora Khaled 2020-11-2

Thank you for your help !

This code works with my problem very well.

But I would like to ask, why check assert(fid>=3,msg)? I thought fid contains the data from the csv file

Stephen23 2020-11-3

编辑：Stephen23 2020-11-3

"But I would like to ask, why check assert(fid>=3,msg)?"

To print an informative error message if the file could not be opened.

"I thought fid contains the data from the csv file"

No, it does not.

The command fopen opens a file and returns a kind of handle to the open file, that handle is known as a "file identifier" (this is explained in the fopen documentation). Then any functions and operators which need to operate on that file (e.g. reading data, writing data, moving the current position in the file, etc.) are given that file ID so that they can perform their operations on the open file.

In this case textscan takes the file ID of an open file and imports the file data using the options that we defined.

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Answer 2

Mathieu NOE 2020-11-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/633399-how-can-i-read-csv-file-data-correctly-i-tried-multiple-ways#answer_531529

在 MATLAB Online 中打开

hello

seems matlab has an issue with the format of your data (especially with )

I could not make it work whatever the options with readtable.

I ended doing a small work around function with basic operations.

Seems to work, at least on my matlab

input data : 4 lines - slightly different - saved as csv file

689d-40bf-9c61-551c0c1a69bf,true,"timestamp"," 2"," 8"," 2",25.21,17.536593101926,39,62

679d-40bf-9c61-551c0c1a69bf,true,"timestamp"," 2"," 8"," 2",25.21,17.536593101926,39,63

669d-40bf-9c61-551c0c1a69bf,true,"timestamp"," 2"," 8"," 2",25.21,17.536593101926,39,64

659d-40bf-9c61-551c0c1a69bf,true,"timestamp"," 2"," 8"," 2",25.21,17.536593101926,39,65

function code as follows :

function output_matrix = retrieve_csv(Filename)
fid = fopen(Filename);
tline = fgetl(fid);
k = 0;
while ischar(tline)
    
    k = k+1;    % loop over line index
    
    sep = findstr(tline,',');
	ind = [0;sep(:);length(tline)+1];
    
	for ci = 1:length(ind)-1
        tline_extract = tline(ind(ci)+1:ind(ci+1)-1);
        % remove undesired characters (")
        ind_rem = findstr(tline_extract,'"');
        tline_extract(ind_rem) = '';
        output_matrix{k,ci} = tline_extract;
	end
    
   
tline = fgetl(fid);
    
end
fclose(fid);

output :

output_matrix =

Columns 1 through 7

[1x27 char] 'true' 'timestamp' ' 2' ' 8' ' 2' '25.21'

Columns 8 through 10

'17.536593101926' '39' '62'

'17.536593101926' '39' '63'

'17.536593101926' '39' '64'

'17.536593101926' '39' '65'

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Nora Khaled 2020-11-2

Thank you very much!

I was wondering how am gonna read the file if no reading function worked, so, this is really helpful.

you can also see Stephen answer, he used the function textscan() with a format specifier.

Mathieu NOE 2020-11-3

yes - I myself learn from Stephen answer ! good for me too !

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How can I read csv file data correctly? I tried multiple ways

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