I have a big text file containing data that needs to be extracted and inserted into a new text file. I possibly need to store this data in an cell/matrix array ?
But for now, the question is that I am trying to test a smaller dataset, to check if the code below works.
I have a code in which it opens a text file, scans through it and replicates the data and saves it in another text file called, "output.txt".
Problem : It doesn't seem to save the file properly. It just shows an empty array in the text file, such as this " [] ". The original text file just contains string of characters.
%opens the text file and checks it line by line.
fid1 = fopen('sample.txt');
tline = fgetl(fid1);
while ischar(tline)
disp(tline);
tline = fgetl(fid1);
end
fclose(fid1);
% save the sample.txt file to a new text fie
fid = fopen('output.txt', 'w');
fprintf(fid, '%s %s\n', fid1);
fclose(fid);
% view the contents of the file
type exp.txt
Where do i go from here ?
It's not a good practice to read an input file by loading all of its contents to memory at once. This way the file size you're able to read is limited by the amount of memory on the machine (or by the amount of memory the OS is willing to allocate to a single process).
Instead, use fopen and its related function in order to read the file line-by-line or char-by- char.
For example,
fid1 = fopen('sample.txt', 'r');
fid = fopen('output.txt', 'w');
tline = fgetl(fid1);
while ischar(tline)
fprintf(fid, '%s\n', tline);
tline = fgetl(fid1);
end
fclose(fid1);
fclose(fid);
type output.txt
Of course, if you know in advance that the input file is never going to be large, you can read it all at once using by textread or some equivalent function.
Try using textread, it reads data from a text file and stores it as a matrix or a Cell array. At the end of the day, I assume you would want the data to be stored in a variable to manipulate it as required. Once you are done manipulating, open a file using fopen and use fprintf to write data in the format you want.
Related
I have a huge .txt file and parts of which I want to parse (using text scan), say I have 10000 line data and a part which starts at line 300, the part also has a header of 10 lines say,how can I skip the first 300 lines(not using header function of text scan of course as I then wont be able to get my actual 10 line header) or is there a way in which I can jump to line 300 and start text scan from there as if 301 line was the first line.
So, assuming your data is generated by the following (since you have not mentioned how it's formatted in your question):
fid = fopen('datafile.txt', 'w');
for i=1:300
fprintf(fid, 'ignore%d\n', i);
end
for i=301:310
fprintf(fid, 'header%d\n', i);
end
for i=311:10000
fprintf(fid, '%d\n', i);
end
fclose(fid);
You can read the data by first using fgetl to advance to the 300th line, then using textscan twice to get the header info and the data. Basically, the thing to remember is that textscan works starting from the place where fid is pointing. So, if it's pointing to the 301st line, it'll start scanning from there. So, here's the code to read the file above, starting from line 301:
fid = fopen('datafile.txt', 'r');
for i=1:300
fgetl(fid);
end
scannedHeader = textscan(fid, '%s', 10);
scannedData = textscan(fid, '%d');
fclose(fid);
NB: if the data is always the same format, you can use ftell to know where to skip to exactly then use fseek to go to that offset.
I have two files, Editor.m and Parameters.m. I want to write a code in Editor.m that when run does the following task:
reads Parameters.m
searches for a line in it (e.g. dt=1)
replaces it with something else (e.g. dt=0.6)
saves Parameters.m.
So, at the end of this process, Parameters.m will contain the line dt=0.6 instead of dt=1, without me having edited it directly.
Is there a way to do this? If so, how?
You can use regexprep to replace the value of interest.
% Read the file contents
fid = fopen('Parameters.m', 'r');
contents = fread(fid, '*char').';
fclose(fid);
% Replace the necessary values
contents = regexprep(contents, '(?<=dt=)\d*\.?\d+', '0.6');
% Save the new string back to the file
fid = fopen('Parameters.m', 'w');
fwrite(fid, contents)
fclose(fid)
If you can guarantee that it will only ever appear as 'dt=1', then you can use strrep instead
contents = strrep(contents, 'dt=1', 'dt=0.6');
I have a very large matrix (M X N). I want to divide matrix into 10 equal parts (almost) and save each of them into a separate file say A1.txt, A2.txt, etc. or .mat format. How can I do this ?
Below is a code to divide a matrix into 10 equal parts and data_size is (M / 10).
for i=1:10
if i==1
data = DATA(1:data_size,:);
elseif i==10
data = DATA((i-1)*data_size+1:end,:);
else
data = DATA((i-1)*data_size+1: i*data_size,:);
end
save data(i).mat data
% What should I write here in order to save data into separate file data1.mat, data2.mat etc.
end
You said you wanted it in either txt format or mat format. I'll provide both solutions, and some of this is attributed to Daniel in his comment in your post above.
Saving as a text file
You can use fopen to open a file up for writing. This returns an ID to the file that you want to write to. After this, use fprintf and specify the ID to the file that you want to write to, and the data you want to write to this file. As such, with sprintf, generate the text file name you want, then use fprintf to write data to your file. It should be noted that writing matrices to fprintf in MATLAB assume column major format. If you don't want your data written this way and want it done in row-major, you need to transpose your data before you write this to file. I'll provide both methods in the code depending on what you want.
After you're done, use fclose to close the file noting that you have finished writing to it. Therefore, you would do this:
for i=1:10
if i==1
data = DATA(1:data_size,:);
elseif i==10
data = DATA((i-1)*data_size+1:end,:);
else
data = DATA((i-1)*data_size+1: i*data_size,:);
end
filename = sprintf('A%d.txt', i); %// Generate file name
fid = fopen(filename, 'w'); % // Open file for writing
fwrite(fid, '%f ', data.'); %// Write to file - Transpose for row major!
%// fwrite(fid, '%f ', data); %// Write to file - Column major!
fclose(fid); %// Close file
end
Take note that I space separated the numbers so you can open up the file and see how these values are written accordingly. I've also used the default precision and formatting by just using %f. You can play around with this by looking at the fprintf documentation and customizing the precision and leading zero formatting to your desire.
Saving to a MAT file
This is actually a more simpler approach. You would still use sprintf to save your data, then use the save command to save your workspace variables to file. Therefore, your loop would be this:
for i=1:10
if i==1
data = DATA(1:data_size,:);
elseif i==10
data = DATA((i-1)*data_size+1:end,:);
else
data = DATA((i-1)*data_size+1: i*data_size,:);
end
filename = sprintf('A%d.mat', i); %// Generate file name
save(filename, 'data');
end
Take note that the variable you want to save must be a string. This is why you have to put single quotes around the data variable as this is the variable you are writing to file.
You can use
save(['data' num2str(i) '.mat'], 'data');
where [ ] is used to concatenate strings and num2str to convert an integer to a string.
I want to load a csv file in a matrix using matlab.
I used the following code:
formatSpec = ['%*f', repmat('%f',1,20)];
fid = fopen(filename);
X = textscan(fid, formatSpec, 'Delimiter', ',', 'CollectOutput', 1);
fclose(fid);
X = X{1};
The csv file has 1000 rows and 21 columns.
However, the matrix X generated has 2000 columns and 20 columns.
I tried using different delimiters like '\t' or '\n', but it doesn't change.
When I displayed X, I noticed that it displayed the correct csv file but with extra rows of zeros every 2 rows.
I also tried adding the 'HeaderLines' parameters:
`X = textscan(fid, formatSpec1, 'Delimiter', '\n', 'CollectOutput', 1, 'HeaderLines', 1);`
but this time, the result is an empty matrix.
Am I missing something?
EDIT: #horchler
I could read with no problem the 'test.csv' file.
There is no extra comma at the end of each row. I generated my csv file with a python script: I read the rows of another csv file, modified these (selecting some of them and doing arithmetic operations on them) and wrote the new rows on another csv file. In order to do this, I converted each element of the first csv file into floats...
New Edit:
Reading the textscan documentation more carefully, I think the problem is that my input file is neither a textfile nor a str, but a file containing floats
EDIT: three lines from the file
0,1,0,0,0,1,0,0,0,1,0,0,0,1,0,0,1,0,0,0,2
1,-0.3834323,-1.92452324171,-1.2453254094,0.43455627857,-0.24571121,0.4340657,1,1,0,0,0,0.3517396202,1,0,0,0.3558122164,0.2936975319,0.4105696144,0,1,0
-0.78676,-1.09767,0.765554578,0.76579043,0.76,1,0,0,323124.235998,1,0,0,0,1,0,0,1,0,0,0,2
How about using regex ?
X=[];
fid = fopen(filename);
while 1
fl = fgetl(fid);
if ~ischar(fl), break, end
r =regexp(fl,'([-]*\d+[.]*\d*)','match');
r=r(1:21); % because your line 2nd is somehow having 22 elements,
% all lines must have same # elements or an error will be thrown
% Error: CAT arguments dimensions are not consistent.
X=[X;r];
end
fclose(fid);
Using csvread to read a csv file seems a good option. However, I also tend to read csv files with textscan as files are sometimes badly written. Having more options to read them is therefore necessary.
I face a reading problem like yours when I think the file is written a certain way but it is actually written another way. To debug it I use fgetl and print, for each line read, both the output of fgetl and its double version (see the example below). Examining the double version, you may find which character causes a problem.
In your case, I would first look at multiple occurrences of delimiters (',' and '\t') and , in 'textscan', I would activate the option 'MultipleDelimsAsOne' (while turning off 'CollectOutput').
fid = fopen(filename);
tline = fgetl(fid);
while ischar(tline)
disp(tline);
double(tline)
pause;
tline = fgetl(fid);
end
fclose(fid);
I am analyzing a set of text in a .txt file. the file has 30 lines and each line contains different phrases both containing text, numbers, and symbols.
what's the best way to import this file into Matlab for analyses
(i.e.: how many Capital I's are in the text file or how many #text phrases are in the file (analyzing tweets on each line)
I think you'd best read the file line-by-line and save each line in a cell of a cell array:
fid = fopen(filename);
txtlines = cell(0);
tline = fgetl(fid);
while ischar(tline)
txtlines{numel(txtlines)+1}=tline;
tline = fgetl(fid);
end
fclose(fid);
This way you can easily access each line with txtlines{ii}.
If you always need to perform operations on the complete text (ie how many a's in the whole text-file, and not per-line), you can of course just throw the lines together in a single variable.
Executing an operation on each line, can be done simply with cellfun, for example counting the number of capital 'I's:
capI_per_line = cellfun(#(str) numel(strfind(str,'I')),txtlines);
If the file is reasonably sized (most 30 line files are) I would read it all into memory at once.
fid = fopen('saturate.m');
str = fread(fid,inf,'*char')';
fclose(fid);
Then, depending on your needs you can use basic matrix operations, string operations or regexp style analysis on the str variable.
For example, "how many capital 'I''s?" is:
numIs = sum(str=='I');
Or, "how many instances of 'someString'?" is:
numSomeString = length(strfind(str, 'someString'));