Inserting Timestamp into a Matrix

Hi all,

The first column of my matrix is a timestamp. How do I get it in a normal date and time format rather than this?

[Star Strider]

What do the data mean?

The ‘2019’ values seem to be years, however ‘-12’ does not seem to be a valid part of a date or time, unless it designates a time zone.

[Megan Stapley]

ONLY first columb is date and time. That is the only column I want to make a timestamp.

[Star Strider]

What are the values that are not ‘2019’? Do they have any significance?

[Megan Stapley]

They are a measurement of data at that time stamp.

Answer 1

[Star Strider]

I still have no idea what you want to do.

However, if you want to concatenate the even rows to the odd rows and have ‘2019’ be the first column in each row, this works:

A = [2019 -12
     0.5    0
     2019 -12
     1      0
     2019 -12
     1.5    0];
 
B = [A(1:2:end,:)  A(2:2:end,:)]

producing:

B =
         2019          -12          0.5            0
         2019          -12            1            0
         2019          -12          1.5            0

If all you have is the year in your time stamp, I would just leave it as is. There is not real benefit to converting it to a datenum or datetime value. However if you absolutely must, this works:

Y = datetime(num2str(B(:,1)), 'InputFormat','yyyy','Format','yyyy');
T = table(Y,B(:,2),B(:,3),B(:,4))                                       % Table

producing:

T =

  3×4 table

     Y      Var2    Var3    Var4
    ____    ____    ____    ____

    2019    -12     0.5      0  
    2019    -12       1      0  
    2019    -12     1.5      0 

Experiment to get the result you want.

Answer 2

[Peter Perkins]

I'm gonna take a wild guess, because there's very little to go on here.

I'm gonna guess you have format short, and you have a matrix each of whose rows is like this

>> x = [2019.012345678 -12 .5 0]
x =
   1.0e+03 *
    2.0190   -0.0120    0.0005         0

I may be wrong. What follows the "2019." may be somethign else. Who knows?

The first thing is, you can't put "time" and "numbers" together in a numeric matrix unless your time is represented as a number, and you already have that. So as Star Strider suggests, you want a table.

>> X = [2019+rand(5,1) randn(5,1)]
X =
   1.0e+03 *
    2.0191    0.0010
    2.0192    0.0005
    2.0192   -0.0000
    2.0194   -0.0000
    2.0190   -0.0008
>> t = array2table(X)
t =
  5×2 table
      X1         X2    
    ______    _________
    2019.1      0.96423
    2019.2      0.52006
    2019.2    -0.020028
    2019.4    -0.034771
      2019     -0.79816
>> t.Year = floor(t.X1);
>> t.YearFrac = t.X1 - t.Year
t =
  5×4 table
      X1         X2        Year    YearFrac
    ______    _________    ____    ________
    2019.1      0.96423    2019     0.12332
    2019.2      0.52006    2019     0.18391
    2019.2    -0.020028    2019     0.23995
    2019.4    -0.034771    2019     0.41727
      2019     -0.79816    2019    0.049654
>> t.Time = datetime(t.Year,1,1) + years(t.YearFrac)
t =
  5×5 table
      X1         X2        Year    YearFrac            Time        
    ______    _________    ____    ________    ____________________
    2019.1      0.96423    2019     0.12332    15-Feb-2019 00:59:29
    2019.2      0.52006    2019     0.18391    09-Mar-2019 04:06:09
    2019.2    -0.020028    2019     0.23995    29-Mar-2019 15:22:50
    2019.4    -0.034771    2019     0.41727    02-Jun-2019 09:41:16
      2019     -0.79816    2019    0.049654    19-Jan-2019 03:15:42
>> tt = table2timetable(t(:,{'Time' 'X2'}))
tt =
  5×1 timetable
            Time               X2    
    ____________________    _________
    15-Feb-2019 00:59:29      0.96423
    09-Mar-2019 04:06:09      0.52006
    29-Mar-2019 15:22:50    -0.020028
    02-Jun-2019 09:41:16    -0.034771
    19-Jan-2019 03:15:42     -0.79816