Time and date fields not correclty imported using readmatrix

I am trying to import csv and dat files that have columns with date and time. Here is a snapshot of csv file:

And dat file:

I am using "readmatrix" method for import. However, upon import, the date and time fields are converted to NaN. Is there a way to read these files while preserving time format? I intend to do some timestamp based filtering and plotting, so the resloution of timestamp is important.

Answer 1

[Cris LaPierre]

You cannot mix data types when you use readmatrix, meaning all the data you import must be of the same data type. That is why you are getting NaN and not NaT.

Use readtable or readtimetable instead. In a table, each column can be a different data type.

[Rakshith Badarinath]

Thanks! readtable works.

When I use readtable on the dat file, it skips certain rows in the beginning. This is OK. However, I want to obtain a specific time stored in the third line of the dat file (see image above). How can I get this value?

I want to use this time to do subtractions in the 'Time' column of the csv file.

[Rakshith Badarinath]

I can use datetime('time string','InputFormat','HH:mm:ss.SSS') to get the Time that can be added or subtracted from table obtained from csv data.

However, the 'time string' is located in the dat file and is always at a fixed position: 3rd row from top and after 'Time: \t' string. Is there a way to read this particular row? I guess i will have to use native file read functions like fopen and fgetl

[Cris LaPierre]

You would have to use a second read command to capture just row 3. Perhaps textscan? I'm not feeling motivated enough to transcribe your image for testing, so here's a best guess at what that might be.

fid = fopen('filename.dat');
% Skip the first string, then read in time as a duration
tm = textscan(fid,'%*s %{hh:mm:ss.SSS}T',1,'HeaderLines',2)
fclose(fid);

tm will be a cell array. You can extract the time value from the cell array like this.

tm=tm{:}

Then use your readtable command to get the matrix of data.

With all your dates as datetimes or durations, you can perform Date and Time arithmetic.

[Rakshith Badarinath]

Thanks. I ended up using fopen with fegetl and regexp to extract the time cell array and converted it to duration. textscan seems compact, will give it a try.