Filter löschen
Filter löschen

how to extract data from an text file?

54 Ansichten (letzte 30 Tage)
isamh
isamh am 3 Feb. 2020
Kommentiert: Walter Roberson am 14 Feb. 2020
I have two files, one in excel and one in a text file, how would i obtain column data from the text file even though i did it from an excel file.
code is:
filename = 'mct.xlsx'
data = xlsread(filename, 'mct', 'A:D');
Phase1 = data(data(:4)==1,:);
how would i be able to extract this from a text file?

Akzeptierte Antwort

fred  ssemwogerere
fred ssemwogerere am 3 Feb. 2020
Hello, there are a number of ways to go about this. Please refer to the following links:
  1 Kommentar
isamh
isamh am 3 Feb. 2020
Bearbeitet: isamh am 3 Feb. 2020
saw this example and had several questions
x = 100*rand(8,1);
fileID = fopen('nums1.txt','w');
fprintf(fileID,'%4.4f\n',x);
fclose(fileID);
what does the 'w' mean?
also, what does ''%4.4f\n'' mean?

Melden Sie sich an, um zu kommentieren.

Weitere Antworten (3)

fred  ssemwogerere
fred ssemwogerere am 4 Feb. 2020
% what does the 'w' mean?
'w' gives write access permission to the file
% also, what does ''%4.4f\n'' mean?
This is a formatting operator that prints each input as a fixed point number having field width of 4, and the number of digits after the decimal point of 4, before proceeding to a new line ("\n").
  8 Kommentare
isamh
isamh am 5 Feb. 2020
Bearbeitet: isamh am 5 Feb. 2020
fid = fopen('MCT_Drive_Traces1.txt', 'rt');
DATA = cell2mat( textscan(fid, '%f%f%f%f', 'Delimiter', '\t', 'HeaderLines', 4) );
fclose(fid);
%% Phase 1
Phase_1 = DATA(DATA(:,4)==1,:);
hey, i tried the code above and noticed that the matrix DATA doesn't contain all the rows it's missing about one fifth of the rows.
Fixed the problem, there were headers between the numbers at some certian rows, would there be a way to ignore all headers except for the first row?
Walter Roberson
Walter Roberson am 5 Feb. 2020
Sometimes you can use textscan CommentStyle to ignore headers if they always have the same start and stop. Otherwise sometimes you end up looping textscan, especially if you want the blocks to be separated in output.
Another method that can be very useful is to fileread() the entire file as a character vector, and then use a combination of regexp and regexprep to extract parts of it, possibly then passing the resulting characters into textscan.

Melden Sie sich an, um zu kommentieren.


isamh
isamh am 5 Feb. 2020
will try that out, thanks for everything Walter!

isamh
isamh am 12 Feb. 2020
Bearbeitet: isamh am 12 Feb. 2020
Hey Walter, I tried to ignore any text that appears within the TXT file but kept getting an error message.
Code:
result = [];
fid=fopen('MCT_Data.txt');
tic
while 1
tline = fgetl(fid);
if ~ischar(tline), break, end
celldata = textscan(tline,'%f %f %f %f %f %f');
matdata = cell2mat(celldata);
% match fails for text lines, textscan returns empty cells
result = [result ; matdata];
end
toc
fclose(fid);
the error message is:
Error using textscan.
First input can not be empty. Expected a non-empty character vector or a valid file-id.
so, the two rows contain
R E V D
m k h -
435 345 435 3543
...
the file has alot of numerical data. the headers repeat randomly and are the same every time they repeat.
how would ignore everything but numerical data?
  3 Kommentare
isamh
isamh am 14 Feb. 2020
would this: if isempty(tline); continue; end be placed after results? or
got this code from another question and it works but takes some time.
str = fileread('MCT_Data.txt');
nums = cellfun(@str2double, regexp(str, '([\d.,]+)', 'match'));
x = reshape(nums, 4, [])';
Walter Roberson
Walter Roberson am 14 Feb. 2020
result = [];
fid=fopen('MCT_Data.txt');
tic
while 1
tline = fgetl(fid);
if ~ischar(tline); break; end %end of file
if isempty(tline); continue; end %empty line
celldata = textscan(tline,'%f %f %f %f %f %f');
matdata = cell2mat(celldata);
% match fails for text lines, textscan returns empty cells
result = [result ; matdata];
end
toc
fclose(fid);
What is your file format? It appears that you have text at the beginning of some of the lines, and you are doing this looping so that you can ignore those lines? There are usually easier ways to deal with such files.

Melden Sie sich an, um zu kommentieren.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by