Read the third column of a .csv file

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Alex Perrakis
Alex Perrakis 2022-4-26
回答： Johannes Hougaard 2022-4-26
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
Walter Roberson
Walter Roberson 2022-4-26
give the option for decimal separator being ','
Alex Perrakis
Alex Perrakis 2022-4-26
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);

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采纳的回答

Mathieu NOE
Mathieu NOE 2022-4-26
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

更多回答（1 个）

Johannes Hougaard
Johannes Hougaard 2022-4-26
Ran in:
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

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