MATLAB Answers

Read specific columns of a text file

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Jessica Thomas
Jessica Thomas on 29 Mar 2016
Edited: Orion on 29 Mar 2016
I have a text file that contains 191 columns and over 64000 rows. Since this is a big file I only want to extract all the rows for the last 5 columns. How would I do this?

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Answers (2)

Robert
Robert on 29 Mar 2016
I recommend you check out datastore.
docsearch Read and Analyze Large Tabular Text File
You can use its SelectedVariableNames property to tell it to read only your desired columns.
You could also use fscanf. An asterisk in the format specifier tells fscanf to skip that field.

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Orion
Orion on 29 Mar 2016
Edited: Orion on 29 Mar 2016
Assume you have this txt file that contains a matrix with 8 columns.
you can read the 5 last columns like this :
% filename
filename = 'mytxtfile.txt';
% pattern to analyse the txt file
formatSpec = [repmat('%*d',1,8-5+1) repmat('%d',1,5) '%[^\n\r]'];
delimiter = ' ';
% read file
fid = fopen(filename,'r');
dataArray = textscan(fileID, formatSpec,'Delimiter', delimiter);
fclose(fileID);
% convert into matrix
MyLast5Columns = cell2mat(dataArray(1:5));
You just have to adapt this to your file (number of columns, type of numbers (float, integer,..)).

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