MATLAB: How can i select daily data with a 15 min partition

databaseMATLABtime series

Hi!!

I have a timetable with data of days with a periodicity of 15 min and I want to select different days. At the time of selecting the days that I want, only get the data for the day at 00:00. I want you to take all the data from those selected days.

Thanks in advance

Best Answer

These two things

"only get the data for the day at 00:00. I want you to take all the data from those selected days"

seem contradictory.

It sounds like you have a timetable that spans multiple days, with 15min time steps. If you want to select only some of those days, and they are contiguous, use timerange as Steve suggests. If the days are not contiguous, use ismember to create a logical vector from the timetable's row times, then use that as a row subscript to select the days of interest.

If you additionally only want the "midnight" rows on those selected days, use timeofday on the timetable's row times to again create a logical vector for subscripting.

If, on the other hand, you want to somehow aggregate all the data from each day into one row whose timestamp is at midnight, use retime with an aggregation, as KSSV suggests.

It would help if you gavce a short clear example of what you have and what you want.

Related Solutions

MATLAB: Hi, i have two dates like 2013_12_28 and 2014_01_06, and i want to calculate the mean date (2014_01_01) which would be in the form of 2014.0014

md = mean(datenum({'2013_12_28', '2014_01_06'}, 'YYYY_mm_dd'));
dv = datevec(md);
days_into_year = md - datenum([dv(1),1,1]);

But once you have days_into_year you have to convert that into a year fraction, which requires careful definition of how long a "year" is. Is a "year" 365 days, always? Is a "year" 365.2421875 days? Is a "year" 365 days for non-leap years but 366 days for leap-years? If so then should it be 365 days for dates in the year before the leap day but 366 for dates on or after the leap day?

Converting to a specific date is much easier, and getting the result in terms of days is easy, but fraction of a year needs clarification.

MATLAB: I have a time table with a year’s worth of current measurements. (Time format is Year-Month-Day-Hour-Min-Sec) How to take each day and count how many times the current was over a specific reading that day.

The method input argument to retime can be a function handle to a function that accepts a vector of data and returns a scalar or row vector. Try writing a function that accepts the data from each day and returns the number of values that are greater than your threshold and passing that into retime as the method input.

Let's start with some random data.

rng default
mpd = minutes(days(1)); % minutes per day
T = datetime('today');
x = randi(mpd, 100, 1); % Minutes after midnight
y = randi(50, 100, 1);

Create a timetable.

tt = timetable(T + minutes(x), y);

Define a function to count number of y values greater than 20 in each bin.

fh = @(data) nnz(data > 20);

Retime the original timetable using the method fh, binning the data by hour.

tt2 = retime(tt, 'hourly', fh);

Let's see how many hours had at least 1 value in the original data greater than 20. Just show the first couple.

H = head(tt2)

Look at the values in tt that fell into the first bin in tt2.

tt(timerange(H.Time(1), H.Time(2)), :)

Since I set rng default at the top, you should see what I do: three values that exceed 20 and one that doesn't in the time between midnight and 1 AM. So the count of 3 in tt2 for that bin is correct.

ans =
  4×1 timetable
            Time            y 
    ____________________    __
    03-Sep-2019 00:52:00    49
    03-Sep-2019 00:46:00    46
    03-Sep-2019 00:50:00     8
    03-Sep-2019 00:18:00    41

Bin 6 (5 AM to 6 AM) of tt has no values of y greater than 20, so the corresponding element in tt2 is 0.

>> tt(timerange(H.Time(6), H.Time(7)), :)
ans =
  2×1 timetable
            Time            y
    ____________________    _
    03-Sep-2019 05:23:00    6
    03-Sep-2019 05:51:00    1
>> tt2(6, :)
ans =
  timetable
            Time            y
    ____________________    _
    03-Sep-2019 05:00:00    0

Best Answer

Related Solutions

MATLAB: Hi, i have two dates like 2013_12_28 and 2014_01_06, and i want to calculate the mean date (2014_01_01) which would be in the form of 2014.0014

MATLAB: I have a time table with a year’s worth of current measurements. (Time format is Year-Month​-Day-Hour-​Min-Sec) How to take each day and count how many times the current was over a specific reading that day.

Related Question

MATLAB: I have a time table with a year’s worth of current measurements. (Time format is Year-Month-Day-Hour-Min-Sec) How to take each day and count how many times the current was over a specific reading that day.