Creating a Loop to Apply a Certain Constant Based on the Month in the Time Series

I have five months of 6-minute water level (WL) data. I am inputing the WL data into this equation to derive a pressure value:

Pressure = (Gravity * Density * WL) / 1000

Gravity is a constant that will remain the same over the five months. My issue is that the density changes from month to month with the following values:

Density1 = 1.01;
Density2 = 1.019; 
Density3 = 1.02;
Density4 = 1.02;
Density5 = 1.017;

With my time series of WL data, I am trying to create a loop that will be able to detect which month the data was recorded in and apply that specific density value to the pressure equation. The reason I am trying to create this loop is because I will eventaully be working with multiple years worth of data. So for example I will have 12 different density values for each month of the year and If I have 4 years of data I will need the loop to loop back around after December and into the next year. If any other information is needed to understand what I am looking for, I am happy to provide more details.

Any help or advice is greatly appreciated!

Thank you

[Morgan]

Could you provide the WL data?

[Lei Hou]

Use datetime('now') returns the current time. Then call month(datetime) to get the month information.

>> datetime('now')

ans = 

  datetime

   18-Nov-2022 11:41:23

>> month(datetime('now'))

ans =

    11

Answer 1

[Santosh Fatale]

Hi Luke,

If you are using timeseries objects for data processing, then please note that timeseries will no longer be supported in a future release. Instead of timeseries objects, you can use timetable.

To convert your timeseries data into timetable format, you can use the timeseries2timetable function.

I assumed that the "Density" changes with the month but not with the year. If you have timeseries data for "WL", you can utilize the following steps to create a loop over the variable "WL":

• Convert timeseries WL data into timetable format.

timetableWL = timeseries2timetable(WL)

• For each entry in WL, you can get information about the month using the function month. The function "month" needs input of type datetime format, which you can retrieve using the following commands from WL timetable.

datetimeData = timetableWL.Properties.RowTimes

• For each month retrieved in the last step, assign a known value of density from lookup table.

Answer 2

[JAT]

Hi Luke, this is an old question but I came across it because I'm looking for a similar answer. I am trying to add a fixed monthly value (so 12 different values) to all the Januarys, February's, etc in a multi-year time series. So I want Matlab to go through and 'know' when it's January and add amount 1, and then 'know' when it's February and add amount 2 - regardless of the day and year. Did you ever solve this question?