how to store a signal along with time in the same matrix?

Hello, I want to know how can i store and present two variables in a single matrix. i have a ECG data file of 1x100000 and a time vector of same size. i want to present them in the same matrix. how can i do that? Also can i add other variables too to the matrix like comments etc. Thank you

Answer 1

[Star Strider]

Concatenate them vertically:

EKG_Record = [time; ECG];

This puts the time vector in row #1 and the electrocardiogram in row #2.

[mahrukh jamil]

Thank you for your answer. I don't know I tried different ways but it was concatenating it horizontally. Now it works. Also now where ever i use this signal, it would give me the time values too?

[Star Strider]

My pleasure.

Horizontal concatenation results from using no operator or the comma (,) operator between the variables. Vertical concatenation results from using the semicolon (;) operator. So for example if variables ‘a’, ‘b’ and ‘c’ are scalars:

v = [a b c];        % Row Vector
v = [a, b, c];      % Row Vector
v = [a; b; c];      % Column Vector

If you want to use the ‘EKG_Record’ variable in other applications as you created it here, save it as a .mat file.

Example:

save('EKG_Record_01.mat', 'EKG_Record')

then whenever you want to use it, load it as, for example:

d = load('EKG_Record_01.mat');

The ‘d’ variable now contains two fields, ‘time’ and ‘ECG’. To use them in your code, create new variables for them:

ECG1 = d.ECG;
t1   = d.time;

This allows you to assign them to specific variables so the variables in the .mat file do not overwrite variables of the same names already in your workspace. See the documentation for the save and load functions for a complete description.

[mahrukh jamil]

Thank you for your detailed explanation. That's really helping. one quick question. If i want to add other rows too, this would be done in the same manner? for example i want to create a new .mat file containing

sampling rate time extracted features comments 'this features belongs to class A'

[Star Strider]

That would work, but not adding them as rows. You would have to add those as separate variables (they could be numeric, string, cell, table, or other variable classes) to ‘EKG_Record_01.mat’:

Ts = ...;                                       % Sampling Interval (sec) (Or However You Define It)
ExtractedFeatures = ...;                        % Whatever You Want
Comments = 'These features belong to class A';  % Comments

save('EKG_Record_01.mat', 'EKG_Record', 'SamplingTime', 'ExtractedFeatures', 'Comments');

They would all be available as separate fields in ‘d’ (in my example code), so you could define them after load or not as you wish. They would be saved in the .mat file and available, whether you need them or not in a specific application.

[mahrukh jamil]

Wow. Thats such a great explanation to my question. Thank you for making things easier for me. Where the variables will be saved in the .mat file. i mean as rows or columns?

[Star Strider]

Thank you. As always, my pleasure.

The variables will be stored in the .mat file exactly as they were in your original workspace. If you created a matrix from two columns, it will be stored as two columns. If you created another one from two rows, it will be stored as two rows. The same applies to cell arrays, table variables, datetime variables, timeseries arrays, and anything else you want to create and then store in your .mat file. You will load them exactly as they were when you save them.

See the documentation for save, load, matfile, and related functions for all the interesting details. It is definitely worthwhile to learn about .mat files because they are so versatile.

[mahrukh jamil]

Oh ok. Yes I will. Thanks for the guides and tips.

[Star Strider]

My pleasure.