Creating time index in timetable

Newer to MATLAB (oringally a Python user) and I am trying to create a table of timeseries water level data and it is proving rather difficult. (Pandas dataframes are 100x easier imo).

So, I have a indexVal = 1x2088 datetime and I am trying to insert it as the row time in a new empty time table that I can then fill with water level values which are of format data = 1x2088 cell. How do I do this? I have tried a few things :

TT = timetable(indexVal);

convert indexVal -> Dates = {indexVal}; then repeat above with dates

Is there a way to create a timetable with just the dates in the first column before adding any data?

I was originally going to create a table and got it or so I thought, but it fills them horizontally instead of vertically and I couldn't get that to transpose correctly.

Any help and advice would be appreciated.

WANT

Time Var1 Var2

------------------------------ | ----- | ----- |

2016-01-05 01:00:00 ( Var columns empty to start)

2016-01-05 02:00:00

2016-01-05 03:00:00

2016-01-05 04:00:00

2016-01-05 05:00:00

THEN append to corresponding var

data = {[0.4857]} {[0.5367]} {[0.5771]} {[0.5969]} {[0.5957]} {[0.5789]} {[0.5485]} {[0.4969]} {[0.4281]} {[0.3488]} {[0.2699]} {[0.1999]} {[0.1405]} {[0.1002]} {[0.0683]} {[0.0454]} {[0.0480]} {[0.0559]} {[0.0832]} {[0.1308]} {[0.1771]} {[0.2296]} {[0.2855]} {[0.3482]} {[0.4167]} {[0.4910]} {[0.5623]} {[0.6185]} {[0.6586]} {[0.6803]} {[0.6805]} {[0.6620]} {[0.6230]} {[0.5631]} {[0.4885]} {[0.4129]} {[0.3437]} ...equivalent length as time

Answer 1

[Peter Perkins]

Autumn, "indexVal = 1x2088" is the problem. Tables are more general than data frames in Python, in that a variable in a table may itself have multiple columns (which is why a table contains "variables", not "columns"). So when you make a table from a 1x2088 variable in your workspace, you get a 1x1 table whose only variable has 2088 length-inbe columns. Ditto for timetables.

On the other hand, the RowTime parameter accepts any vector. So, these are equivalent:

>> tt = timetable('RowTimes',datetime(2022,3,7:10))
tt =
  4×0 empty timetable
>> tt = timetable(datetime(2022,3,7:10)')
tt =
  4×0 empty timetable

and then add data as you wish:

>> tt.X = [1;2;3;4]
tt =
  4×1 timetable
       Time        X
    ___________    _
    07-Mar-2022    1
    08-Mar-2022    2
    09-Mar-2022    3
    10-Mar-2022    4
>> tt.Y = ["one";"two";"three";"four"]
tt =
  4×2 timetable
       Time        X       Y   
    ___________    _    _______
    07-Mar-2022    1    "one"  
    08-Mar-2022    2    "two"  
    09-Mar-2022    3    "three"
    10-Mar-2022    4    "four" 

Or even

>> [tt array2table(rand(4,2))]
ans =
  4×4 timetable
       Time        X       Y         Var1       Var2  
    ___________    _    _______    ________    _______
    07-Mar-2022    1    "one"       0.82119    0.64912
    08-Mar-2022    2    "two"      0.015403    0.73172
    09-Mar-2022    3    "three"    0.043024    0.64775
    10-Mar-2022    4    "four"      0.16899    0.45092

Also, not sure how you ended up with it, but you really don't want to have

    data =     {[0.4857]}    {[0.5367]}    {[0.5771]}    {[0.5969]} ...

That's a cell array containing scalar numeric. You want a double vector. You should figure out how you got that, but for now cell2num will get you out of there.

[Autumn P]

Hi Peter, I appreciate the information. Most of this is readily available on the Mathworks site. I tried using the "RowTImes' and it did not work with the indexVal I have as you said it is the problem. So that means I need to convert it to another format. I do not want to just randomly generate dates or a few consecutive dates, they are coming from a model output. How would you propose I convert or initially store my list of datetimes from my document so that it will align with this method or the table method? I don't think I am advanced enough in Matlab to know how do this from what you have given here.

Yea, Matlab is confusing me coming from Python and the formats are all wonky. I converted data from a num2cell when I was originally trying to create a table because it didn't like the double vector.

[Peter Perkins]

What I said is that you should not be using row vectors, you should be using column vectors. You may simply need to transpose your vectors.

x = 1:5 is a row vector. x = (1:5)' is a column vector.

You have said several times that what you have done isn't working, but you have not shown what you have done. Hard to give specific advice, but nothing you have described should be at all difficult or complicated. For example, what went wrong that led you to use num2cell?