Create a time table

Hey guys, thanks in advance.

I have a program that reads samples from a hardware receiver. When it starts receiving I use:

dev.start();
fprintf('Start of LimeSDR\n');
tic;
start_time=datestr(now);

Then it receives this samples:

indRx1 = 1;  % index of the last received sample

[samples1, ~, samplesLength1]             = dev.receive(Fs*Ts,1);
bufferRx1(indRx1:indRx1+samplesLength1-1)   = samples1;

pause(1)
tempo_rececao=toc;
stop_time=datestr(now);

and stops receiving:

% Cleanup and shutdown by stopping the RX stream and having MATLAB delete the handle object.
dev.stop();
clear dev;
fprintf('Stop of LimeSDR\n');

I want to create a timetable that has start time, stop time, Fs(frequency sampling), and samples1(number of samples).

I have done this

TT=array2timetable(samples1,'SampleRate',Fs,'StartTime',start_time);

But this only gives me a column with start time and the samples. How can I do this,

Thank you

[Eric Sofen]

Timetable works with datetime and duration data types, but not datestr, so your start_time and stop_time should be:

start_time = datetime("now");

I'm unclear on your question. Do you want separate variables in the timetable for start_time and stop_time? What is the height of samples1? Are you ending up a one-row timetable in TT?

[Miguel Albuquerque]

I would like that the table, had one one column the time( start_time :stop_time), then on another column the samples 1, I made the test and I was getting 2 columns. The first one with time had the start_time but ended up in a time different from stop time, and on another column I had the samples( 100000 samples).

I changed start_time and stop_time to this:

start_time=datetime('now','Format','dd-MMM-uuuu HH:mm:ss.SSS');
stop_time=datetime('now','Format','dd-MMM-uuuu HH:mm:ss.SSS');

Answer 1

[Ishaan Mehta]

Hi Miguel

From your last comment, as per my understanding, you want to record start_time and end_time in the same column, and then samples1 and fs in other columns in a timetable.

A timetable is a MATLAB datatype which associates a timestamp with each of the rows stored in it.

Please have a look at MATLAB timetable datatype documentation.

According to me, you can go for the table datatype for a single column storing both the start_time and end_time.

For using timetable datatype, the start_time and end_time must be in different columns.

Incase you want to store the time-duration between start_time and stop_time in the first column, that can be done by subtracting start_time from the end_time as demonstrated in the code below.

You can use the following code as a reference.

table1 = table; % table with start_time and end_time in same column
table2 = table; % table with time-duration in first column
table3 = table; % table with start_time and end_time in separate columns

for i = 1:3
    fs = 10; % dummy fs
    samples1 = 100; % dummy samples1
    start_time = datetime('now'); 
    stop_time = datetime('now') + seconds(i*2); % dummy stop_time
 
    % Variables above are initialised to dummy values for demonstration.
    % You should get all the variables above from your own program only,
    % before the following code is executed

    nRows = height(table2);
    table1 = [table1; table(string(start_time) + " : " + string(stop_time), samples1, fs)];
    table2 = [table2; table(stop_time - start_time, samples1, fs)];
    table3 = [table3; table(start_time, stop_time, samples1, fs)];
end

% rename table columns
table1.Properties.VariableNames = ["time" "samples" "frequency"];
table2.Properties.VariableNames = ["time duration" "samples" "frequency"];

table1

table1 = 3×3 table
                        time                         samples    frequency
    _____________________________________________    _______    _________

    "25-Jun-2022 15:13:39 : 25-Jun-2022 15:13:41"      100         10    
    "25-Jun-2022 15:13:39 : 25-Jun-2022 15:13:43"      100         10    
    "25-Jun-2022 15:13:39 : 25-Jun-2022 15:13:45"      100         10    

table2

table2 = 3×3 table
    time duration    samples    frequency
    _____________    _______    _________

      00:00:02         100         10    
      00:00:04         100         10    
      00:00:06         100         10    

table3

table3 = 3×4 table
         start_time              stop_time          samples1    fs
    ____________________    ____________________    ________    __

    25-Jun-2022 15:13:39    25-Jun-2022 15:13:41      100       10
    25-Jun-2022 15:13:39    25-Jun-2022 15:13:43      100       10
    25-Jun-2022 15:13:39    25-Jun-2022 15:13:45      100       10

Hope it helps,

Ishaan Mehta