String to raw data conversion problem (Timestamp Data)

Ok so this one is bugging me a little and hopefully someone has come across this particular issue before:

I have an Arduino thats logging sensor data and i have it dumping the serial data to a log file for parsing and analysis. Part of the log data is the timestamp (as I assume many people would use.)

(Note: I am aware of the Arduino tools for matlab, I have chosen to route the data this way for specific reasons)

Now, I have the data extracted into MATLAB fine, the timestamp and associated data points drop in a table upon extraction and I am able to manipulate the raw numbers without issue. HOWEVER! The timestamp is obviously in a format that MATLAB does not immediate recognize. To compensate for this I used table2array() then extractBetween() to carve out the specific hh:mm:ss portion of the data into a new array variable.

% extract relevant time data as substring
% only hh:mm:ss required for analysis
var_timestamp_raw = data(:,1);
var_timestamp_array = table2array(var_timestamp_raw)
var_timestamp_data = extractBetween(var_timestamp_array, 13, 20)

This is where is gets problematic. The data is still sitting there like a srtring and I then removed the remaining punctuation, to get int values but there you see the problem is that the values are no longer representative of a real time stamp.

"[2020-11-07 14:35:52.417] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "

So basically, my conundrum: Take this column of data (as shown above) and be able to use it as a plotable value against the sensor data im capturing at the same time.

I have read so many variations of working with timestamps my head is honestly starting to spin as everyone has a differnet take on it.

I need as simply as is possible, the timestamp data converted into a value I can plot against... Does anyone have any ideas?

Answer 1

[Pranav Verma]

Hi Stuart,

I have tried converting the string values of the timestamps into a datetime array using simple string parsing:

st = ["[2020-11-07 14:35:52.417] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "
"[2020-11-07 14:35:52.418] "];
 
dstmp = [];
 
st = erase(st,'[');
st = erase(st,']');
c = deblank(st);
 
for i=1:length(st)
    tmp = datetime(c(i) ,'InputFormat','yyyy-MM-dd HH:mm:ss.SSS');
    dstmp = [dstmp tmp];
end

This returns a datetime array st.

To plot the data with timestamps, you can refer to the below discussion thread on the same lines:

https://www.mathworks.com/matlabcentral/answers/314361-plotting-data-with-timestamps

Thanks

[Stuart Duff]

Hi Pranav,

Thank you very much, ill plug this in a see what I can do with the plotting afterward.

Cheers!

Answer 2

[Eric Sofen]

Even simpler...you don't need to strip off the leading and trailing brackets. Datetime can parse formats with character literals if they're specified in the format:

>> datetime(st,"InputFormat","[uuuu-MM-dd HH:mm:ss.SSS] ")
ans = 
  7×1 datetime array
   07-Nov-2020 14:35:52
   07-Nov-2020 14:35:52
   07-Nov-2020 14:35:52
   07-Nov-2020 14:35:52
   07-Nov-2020 14:35:52
   07-Nov-2020 14:35:52
   07-Nov-2020 14:35:52

[Stuart Duff]

That.

Is.

Perfect.