MATLAB Answers

0

Find specific date/time from a series of datenums

Asked by Louise Wilson on 16 Sep 2019
Latest activity Edited by Louise Wilson on 17 Sep 2019
I have a 7184x72001 double matrix where the first column is a list of serial datenumbers.
I am happy to keep the format this way, but I need to be able to select a specific date/time from this list so that I can extract the data from certain days/times that I am interested in.
So, is it either possible to:
-search from a list of datenums to find a specific date/time that I provide?
-add a column of str data to a matrix of double?
or-convert all of the datenums to date and time?
I have tried the second approach so far:
D=csvread('Tiritiri5280_PSD_1sHammingWindow_50%Overlap_output.csv'); %load in data
t=D(:,1); %extract time column
formatOut='yymmddHHMMSS';
times=datestr(t, formatOut); %convert t column datenums to date and time
rows=(1:length(times)).'; %number of dates and times we have
D_new=[rows D]; %add new column to D
D_new(:,1)=timeslist(:,2); %add times in different format to D
-this works but I now get the datenum in a different format which is also not readable. How do I keep the date time in yymmddhhmmss in a double matrix? Is this possible?
Here,column 1 is the new dates/times that I tried to insert in readable form, and column 2 is serial datenum.

  2 Comments

Hi,
in a matrix, you have the problem that you can only have 1 data type for all your data. Maybe a cell array could help you?
Thank you Nicolas, I realised this shortly after asking the question. Woops-from Steven's answer, I think I will try to go with a timetable and see if that is more useful.

Sign in to comment.

Products


Release

R2018b

2 Answers

Answer by Steven Lord
on 17 Sep 2019
 Accepted Answer

If you're going to be doing a lot of processing of this data based on the times, consider turning your column of date numbers into a datetime array and using that datetime array to convert your data matrix into a timetable. Once you do this you could extract data from the timetable based on the times for each row using a timerange as shown in the "Subscript on Time Range" section on this documentation page. You could also resample or aggregate your timetable data using a certain time basis, as shown here.

  1 Comment

Thank you Steven. I would follow these steps to do this?:
t = datetime(X,'ConvertFrom','datenum')
TT = array2timetable(X,'RowTimes',rowTimes)
Would this work, given the values populated in my cells? They are decibel values with five decimal places.
I'm not sure why I am using datenum to be honest... I started my Matlab endeavors using code from a past grad student at the lab where I am working (to answer the same questions but with different data) and all of her code uses those, for some reason I am yet to figure out. My raw date/time data comes in the format yyddmmHHMMSS. Can you convert this format directly to datetime? Also, using a timetable, am I able to use the rowtimes? I'd like to plot them as the x-axis values in a plot.

Sign in to comment.


Answer by Ted Shultz
on 17 Sep 2019

It looks like the start of your approach is reasonable. Once you make a “times” array, there is no need to add it back to the “D” matrix. You can use that as your index.
For example:
indexOfInterest = (times > t_one) && (times < t_two);
someData =d(indexOfInterest, :);

  1 Comment

Sign in to comment.