how to extract data from an text file?

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?

Answer 1

[fred ssemwogerere]

Hello, there are a number of ways to go about this. Please refer to the following links:

https://mathworks.com/help/matlab/ref/fscanf.html

https://mathworks.com/help/matlab/ref/importdata.html

[isamh]

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?

Answer 2

[fred ssemwogerere]

% 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").

[isamh]

this is the code i used,

for x, what if i dont know the # of rows? # of columns will be 4 for sure but how would i make it read the # of rows automatically.

x=rand(4,30000);
fileID = fopen('MCT_Drive_Traces.txt','w');
fprintf(fileID,'%4.4f\n',x);%adjust according to # of columns
fclose(fileID);
T = .1;      

these are the error messages that i get:

1) Index in position 2 exceeds

array bounds (must not

exceed 1).

2) Error in Untitled (line 20)

Phase_1 =

fileID(fileID(:,4)==1,:);

thanks again for the help!

[Walter Roberson]

dlmwrite('MCT_Drive_Traces.txt', x, 'delimiter', ' ', 'precision', 4)

You might possible prefer 'delimiter', '\t' for tabs between columns.

[isamh]

thanks!

i got this error:

Error using dlmwrite (line

104)

\t is not a valid

attribute or delimiter.

Delimiter must be a single

character.

code is:

dlmwrite('MCT_Drive_Traces.txt', x, 'delimiter', ' \t', 'precision', 4)
%% Phase 1
Phase_1 = dlmwrite(dlmwrite(:,4)==1,:);

for phase_1, i want to obtain only 1 on the fourth column including the rows associated with that column

[Walter Roberson]

You have space tab for delimiter; it looks like you need '\t'

Phase_1 = dlmwrite(dlmwrite(:,4)==1,:);

??? You are trying to call the function dlmwrite() passing in a colon as the first parameter ??

dlmwrite('Phase_1.txt', x(x(:,4)==1,:), 'delimiter', 't', 'precision', 4)

[isamh]

thanks for everything! got it to work

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,:);

[Walter Roberson]

delimiter '\t' not 't'

[isamh]

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]

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.

Answer 3

[isamh]

will try that out, thanks for everything Walter!

Answer 4

[isamh]

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?

[Walter Roberson]

fgetl returns something that is not a character when it reaches end of file.

fgetl can return empty if the only thing on a line is the line terminator.

if isempty(tline); continue; end

[isamh]

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]

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.