How to load numbers from a text file to a .mat file?

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I have a text file in the following format. How can I load it to a .mat file in its present form?
5
3
3 2 3 4
2 -1 5
3 1 -3 -4
  4 Comments
Walter Roberson
Walter Roberson on 6 Jan 2022
The only way to get it "exactly like it comes from the file" is in text form.
MATLAB does not have any way to represent arrays that have varying numbers of columns per row (or varying number of rows per column.) There is no way, in MATLAB, to represent "holes" -- you cannot, for example, have a matrix
3 2 3 4
2 -1 5 <hole>
3 1 -3 -4
The closest you can get would be to put NaN in the empty locations.
Sweet Nemesis
Sweet Nemesis on 6 Jan 2022
I am ok with filling the missing values with zero or NaN to make a square matrix. How is that accomplished?

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Accepted Answer

Walter Roberson
Walter Roberson on 6 Jan 2022
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/855395/text.txt';
data = readmatrix(filename)
data = 3×4
3 2 3 4 2 -1 5 NaN 3 1 -3 -4
  2 Comments
Sweet Nemesis
Sweet Nemesis on 6 Jan 2022
Thank you! Is there a way to get the first two lines included in the matrix?
Walter Roberson
Walter Roberson on 6 Jan 2022
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/855395/text.txt';
opts = detectImportOptions(filename);
opts.DataLines = [1 inf];
data = readmatrix(filename, opts)
data = 5×4
5 NaN NaN NaN 3 NaN NaN NaN 3 2 3 4 2 -1 5 NaN 3 1 -3 -4

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More Answers (2)

Mathieu NOE
Mathieu NOE on 6 Jan 2022
hi
maybe this
(I assumed you want each individual value stored in a cell)
the cell array can be of course saved to a mat file
a = readcell('data.txt',"Delimiter"," ")
a = 5×4 cell array
{[5]} {1×1 missing} {1×1 missing} {1×1 missing}
{[3]} {1×1 missing} {1×1 missing} {1×1 missing}
{[3]} {[ 2]} {[ 3]} {[ 4]}
{[2]} {[ -1]} {[ 5]} {1×1 missing}
{[3]} {[ 1]} {[ -3]} {[ -4]}
save test.mat a
  1 Comment
Sweet Nemesis
Sweet Nemesis on 6 Jan 2022
Will this load like a matrix for operations? I am gettting a 1X4 cell with metadata.

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Voss
Voss on 6 Jan 2022
You can read the file into a character array called text and save it to a .mat file:
% read characters from text file:
fid = fopen('text.txt');
text = fread(fid,'*char').';
fclose(fid);
% save to mat:
save('text.mat','text');
Then load the .mat file to check that it is the same as the text file:
S = load('text.mat');
disp(S.text);
5 3 3 2 3 4 2 -1 5 3 1 -3 -4
  2 Comments
Sweet Nemesis
Sweet Nemesis on 6 Jan 2022
Will this load like a matrix? I need integers for the algorithm I'm using.

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