MATLAB: Converting HH:MM:SS into decimal days to make a time series

converting into decimal dayshh:mm:ss to decimal daystimeseries

I need to make a timeseries across three days (7th June – 9th June 2010) – I'm unsure how to include both the time and days across the x-axis?
I think I need to convert into decimal days but I'm unsure on how to do this and combine both days and time.
Seperate timeseries plots need to be made for the mean phosphate and nitrate concentrations in surface and bottom waters, again I'm not sure how to do this!
Any help will be grateful, the excel sheet is attached.

Best Answer

Use a datetime. When you plot, your data type is honored. You can use xtickformat to format how the data appears.
% Define date and time formats for import
opts = detectImportOptions("CTD12-17.xlsx");
% nice, but not necessary
opts.VariableNamingRule = "preserve";
opts = setvartype(opts,"Time","duration");
opts = setvaropts(opts,"Time","InputFormat","hh:mm:ss","DurationFormat","hh:mm:ss");
% Set datetime format for Date + Time
opts = setvartype(opts,"Date_TimeCombined","datetime");
opts = setvaropts(opts,"Date_TimeCombined","InputFormat","dd/MM/yy HH:mm:ss");
% Load data
data = readtable("CTD12-17.xlsx",opts)
data = 6x7 table
       Date          Time      Date + Time Combined    Bottom Water Mean N+N    Surface Water Mean N+N    Bottom Water Mean P    Surface Water Mean P
    ___________    ________    ____________________    _____________________    ______________________    ___________________    ____________________

    07-Jul-2010    04:55:00     07/07/10 04:55:00              10.24                     5.38                    0.68                    0.43        
    07-Jul-2010    15:06:38     07/07/10 15:06:38               8.77                     3.11                    0.64                     0.5        
    07-Jul-2010    22:21:32     07/07/10 22:21:32               9.86                     4.84                    9.67                    0.39        
    08-Jul-2010    04:12:44     08/07/10 04:12:44               9.86                     4.84                    0.67                    0.39        
    08-Jul-2010    20:31:47     08/07/10 20:31:47               9.81                      4.4                    0.71                    0.38        
    09-Jul-2010    02:35:24     09/07/10 02:35:24              10.46                     3.43                     0.7                    0.32        

%Plot
plot(data.("Date + Time Combined"),data.("Bottom Water Mean N+N"))
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