Create a function to extract data several csv files

Question

Milagros ARIETTI 2015-10-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/249693-create-a-function-to-extract-data-several-csv-files

评论： Milagros ARIETTI 2015-10-21

Hello! I´ve been trying to use the Import data/create a function to select a part of my csv files. I want to take matrix of data from a lot of different files. The layout is always the same, so I read tutorials. I try with: http://nl.mathworks.com/help/matlab/import_export/import-data-interactively.html But I get Undefined function 'importfile' for input arguments of type 'char'.

I want, if it is possible a function to use is several csv files. I want to create the matrix numbers. I have a lot of files to run. Can it be done? I think I have a problem to make matlab understand how to change to other files. If I use Import script I get the data but only for that one csv file I used. Not for others.

I am really new at these, any help is a lot! thank you.

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Milagros ARIETTI 2015-10-20

在 MATLAB Online 中打开

function [VarName3,VarName4] = importfile(filename, startRow, endRow) %IMPORTFILE Import numeric data from a text file as column vectors. % [VARNAME3,VARNAME4] = IMPORTFILE(FILENAME) Reads data from text file % FILENAME for the default selection. % % [VARNAME3,VARNAME4] = IMPORTFILE(FILENAME, STARTROW, ENDROW) Reads data % from rows STARTROW through ENDROW of text file FILENAME. % % Example: % [VarName3,VarName4] = importfile('WT01.csv',21, 352); % % See also TEXTSCAN.

% Auto-generated by MATLAB on 2015/10/20 13:20:25

%% Initialize variables. delimiter = ';'; if nargin<=2 startRow = 21; endRow = 352; end

%% Format string for each line of text: % column3: double (%f) % column4: double (%f) % For more information, see the TEXTSCAN documentation. formatSpec = '%*s%*s%f%f%*s%*s%*s%*s%*s%*s%[^\n\r]';

%% Open the text file. fileID = fopen(filename,'r');

%% Read columns of data according to format string. % This call is based on the structure of the file used to generate this % code. If an error occurs for a different file, try regenerating the code % from the Import Tool. dataArray = textscan(fileID, formatSpec, endRow(1)-startRow(1)+1, 'Delimiter', delimiter, 'HeaderLines', startRow(1)-1, 'ReturnOnError', false); for block=2:length(startRow) frewind(fileID); dataArrayBlock = textscan(fileID, formatSpec, endRow(block)-startRow(block)+1, 'Delimiter', delimiter, 'HeaderLines', startRow(block)-1, 'ReturnOnError', false); for col=1:length(dataArray) dataArray{col} = [dataArray{col};dataArrayBlock{col}]; end end

%% Close the text file. fclose(fileID);

%% Post processing for unimportable data. % No unimportable data rules were applied during the import, so no post % processing code is included. To generate code which works for % unimportable data, select unimportable cells in a file and regenerate the % script.

%% Allocate imported array to column variable names VarName3 = dataArray{:, 1}; VarName4 = dataArray{:, 2};

if true
  % code
end

*and after that I try adding*

numFiles = 4; startRow = 21; endRow = 532; myData = cell(1,numFiles);

for fileNum = 1:numFiles fileName = sprintf('WT%01d.csv',fileNum); myData{fileNum} = importfile(fileName,startRow,endRow); end

Milagros ARIETTI 2015-10-21

在 MATLAB Online 中打开

function WT01 = importfile1(filename, startRow, endRow)
%IMPORTFILE1 Import numeric data from a text file as a matrix.
%   WT01 = IMPORTFILE1(FILENAME) Reads data from text file FILENAME for the
%   default selection.
%
%   WT01 = IMPORTFILE1(FILENAME, STARTROW, ENDROW) Reads data from rows
%   STARTROW through ENDROW of text file FILENAME.
%
% Example:
%   WT01 = importfile1('WT01.csv', 21, 532);
%
%    See also TEXTSCAN.
% Auto-generated by MATLAB on 2015/10/21 14:40:29
%%Initialize variables.
filename = 'C:\Users\Milagros\Desktop\Pruebas\0100\New folder\WT%d%d.csv';
delimiter = ';';
if nargin<=2
    startRow = 21;
    endRow = 532;
end
%%Format string for each line of text:
%   column3: double (%f)
% For more information, see the TEXTSCAN documentation.
formatSpec = '%*s%*s%f%*s%*s%*s%*s%*s%*s%*s%[^\n\r]';
%%Open the text file.
fileID = fopen(filename,'r');
%%Read columns of data according to format string.
% This call is based on the structure of the file used to generate this
% code. If an error occurs for a different file, try regenerating the code
% from the Import Tool.
dataArray = textscan(fileID, formatSpec, endRow(1)-startRow(1)+1, 'Delimiter', delimiter, 'HeaderLines', startRow(1)-1, 'ReturnOnError', false);
for block=2:length(startRow)
    frewind(fileID);
    dataArrayBlock = textscan(fileID, formatSpec, endRow(block)-startRow(block)+1, 'Delimiter', delimiter, 'HeaderLines', startRow(block)-1, 'ReturnOnError', false);
    dataArray{1} = [dataArray{1};dataArrayBlock{1}];
end
%%Close the text file.
fclose(fileID);
%%Post processing for unimportable data.
% No unimportable data rules were applied during the import, so no post
% processing code is included. To generate code which works for
% unimportable data, select unimportable cells in a file and regenerate the
% script.
%%Create output variable
WT01 = table(dataArray{1:end-1}, 'VariableNames', {'VarName3'});

I've been trying different things taking the import function and the comments. I can't make it work, these last one says:

Error using textscan Invalid file identifier. Use fopen to generate a valid file identifier.

Error in scotopic (line 36) dataArray = textscan(fileID, formatSpec, endRow(1)-startRow(1)+1, 'Delimiter', delimiter, 'HeaderLines', startRow(1)-1, 'ReturnOnError', false);

Could someone help me with these.

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Answer 1

Milagros ARIETTI 2015-10-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/249693-create-a-function-to-extract-data-several-csv-files#answer_196704

Thank you so much for your answers!

I will upload a file so you can see.

What I need is to take the data from different columns and rows to work with them after. Example. Take C21:J532, C556:H1067, C1089:H1600

After I will need to work on that matrix.

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Answer 2

TastyPastry 2015-10-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/249693-create-a-function-to-extract-data-several-csv-files#answer_196702

在 MATLAB Online 中打开

Place all the files you need to work with in your current directory and use

files = dir('*.csv');

This will list all the .csv files in your folder and you can loop through them using a function of your choosing.

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Guillaume 2015-10-20

编辑：Guillaume 2015-10-20

在 MATLAB Online 中打开

There is no need to place the files in the current directory and I would advise against that as it's a good way to loose some files in the process. dir happily works in any directory:

files = dir(fullfile('c:\path\to\folder', '*.csv'));

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