Read the third column of a .csv file

Question

Alex Perrakis 2022-4-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1705535-read-the-third-column-of-a-csv-file

回答： Johannes Hougaard 2022-4-26

采纳的回答： Mathieu NOE

MS1.csv

在 MATLAB Online 中打开

Hello Guys and Girls,

i have following .csv file and i am trying to import only the 3rd column which is a temperature. The problem is that although i read it with readtable for some reasons my delimiter does not work and it shows the time and temperature in one cell

My code until now is as follows:

URL = uigetdir('C:\_Daten\Messungen\');
  measurements = dir(URL); measurements(1:2) = [];
   file=fullfile( URL, measurements.name);
   
fid = fopen(file, 'rt');
%a = textscan(fid, '%{yyyy-MM-dd}D %{hh:mm:ss.SSS}T  %f ','Delimiter',' ');
 A=readtable(file,'Format','%s%s%n','Delimiter',' ');
 B=table2array(A(:,2));
 C=split(B,' ');
% B=table2array(A(:,3));
% Data = str2double(strrep(B, ',', '.'));
% format short g
fclose(fid);

Thanks very much for the help!

2 个评论
显示无隐藏无

Walter Roberson 2022-4-26

give the option for decimal separator being ','

Alex Perrakis 2022-4-26

在 MATLAB Online 中打开

Hello Walter,

i think 'DecimalSeparator' does not work with readtable, or maybe i am doing sometimg wrong.

URL = uigetdir('C:\_Daten\Messungen\');
  measurements = dir(URL); measurements(1:2) = [];
   file=fullfile( URL, measurements.name);
   
fid = fopen(file, 'rt');
a = textscan(fid, '%q%q%f ','Delimiter','\b\t');
stringData = strrep(fid,',','.');
 A=readtable(file,'DecimalSeparator',',','Format','%s%s%n','Delimiter','\b\t');
 B=table2array(A(:,2));
 C=split(B,' ');
% B=table2array(A(:,3));
% Data = str2double(strrep(B, ',', '.'));
% format short g
fclose(fid);

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Mathieu NOE 2022-4-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1705535-read-the-third-column-of-a-csv-file#answer_951365

在 MATLAB Online 中打开

hello

you can use the import wizard to help you create the right import options for readtable

see demo below - temperature is now in C

file = 'MS1.csv';
A = importfile(file);
C=table2array(A(:,3)); % temperature
function T = importfile(filename, dataLines)
%IMPORTFILE Import data from a text file
%  MS1 = IMPORTFILE(FILENAME) reads data from text file FILENAME for the
%  default selection.  Returns the data as a table.
%
%  MS1 = IMPORTFILE(FILE, DATALINES) reads data for the specified row
%  interval(s) of text file FILENAME. Specify DATALINES as a positive
%  scalar integer or a N-by-2 array of positive scalar integers for
%  dis-contiguous row intervals.
%
%  Example:
%  MS1 = importfile("C:\Users\A0H36019\Documents\MS1.csv", [1, Inf]);
%
%  See also READTABLE.
%
% Auto-generated by MATLAB on 26-Apr-2022 14:43:08
%% Input handling
% If dataLines is not specified, define defaults
if nargin < 2
    dataLines = [1, Inf];
end
%% Set up the Import Options and import the data
opts = delimitedTextImportOptions("NumVariables", 3);
% Specify range and delimiter
opts.DataLines = dataLines;
opts.Delimiter = ["\t", " "];
% Specify column names and types
opts.VariableNames = ["VarName1", "VarName2", "VarName3"];
opts.VariableTypes = ["datetime", "string", "double"];
% Specify file level properties
opts.ExtraColumnsRule = "ignore";
opts.EmptyLineRule = "read";
opts.ConsecutiveDelimitersRule = "join";
% Specify variable properties
opts = setvaropts(opts, "VarName2", "WhitespaceRule", "preserve");
opts = setvaropts(opts, "VarName2", "EmptyFieldRule", "auto");
opts = setvaropts(opts, "VarName1", "InputFormat", "yyyy-MM-dd");
opts = setvaropts(opts, "VarName3", "TrimNonNumeric", true);
opts = setvaropts(opts, "VarName3", "DecimalSeparator", ",");
opts = setvaropts(opts, "VarName3", "ThousandsSeparator", ".");
% Import the data
T = readtable(filename, opts);
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Johannes Hougaard 2022-4-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1705535-read-the-third-column-of-a-csv-file#answer_951415

在 MATLAB Online 中打开

MS1.csv

Another option which requires less of a custom function but still use the 'detectImportOptions' is to specify in your detectImportOptions that the decimal separator is comma

opts = detectImportOptions('MS1.csv','DecimalSeparator',',');
datatable = readtable('MS1.csv',opts);
head(datatable)
ans = 8×3 table
       Var1           Var2        Var3
    __________    ____________    ____

    2022-04-22    10:40:45.763    24.7
    2022-04-22    10:41:23.875    24.4
    2022-04-22    10:42:01.898    24.6
    2022-04-22    10:42:39.999    24.7
    2022-04-22    10:43:18.065    24.6
    2022-04-22    10:43:56.145    24.7
    2022-04-22    10:44:34.208    24.4
    2022-04-22    10:45:12.214    24.7