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Matlab dates and time not aligning after combining

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Callie
Callie 2023-11-14
评论： Peter Perkins 2023-11-16
My end goal is to plot discharge over time with a large dataset. The sample interval for discharge is in minutes and changes from every 5 hours to every 5 minutes a couple years into data collection. I have created a table containing date and time combined and discharge. For some reason when I do this minutes will return to 0 randomly. I am not sure how to fix this so my plot will look normal. The file is too large I cannot import it so I attcahed a screenshot of the original data table and of T. Thanks in advance!!
dataTable = readtable(csvFilePath);
Date=datetime(dataTable{:,16})+minutes(dataTable{:,9});
Discharge=dataTable(:,10);
Q =[Discharge]
Hour=dataTable(:,9)
T_cell = table2array(Q);
Hour_cell=table2array(Hour);
times = datenum(Hour_cell);
t = table(Date,times);
dates = datetime(t.Date,'Format','MM/dd/yyyy HH:mm:SS');
times = datetime(t.times,'ConvertFrom','datenum','Format','MM/dd/yyyy HH:mm:SS');
fullt = dates+timeofday(times);
t.DatesNTimes = fullt;
T=table(fullt, T_cell);
  3 个评论
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Callie
Callie 2023-11-14
Sorry I am new to Matlab. Instead of using the times part I stuck with Hour_cell and still got the same result.
Les Beckham
Les Beckham 2023-11-14
Can you post a subset of the "too large" dataset that illustrates the issue?

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采纳的回答

Cris LaPierre
Cris LaPierre 2023-11-15
编辑：Cris LaPierre 2023-11-15
Ran in:
One issue is that your RecHour variable is not minutes. It is time of day in military time format (no colon. Should be 4 numbers, but that's likely lost due to converstion to numeric data type). The point is it is not appropriate to use minute(dataTable{:,9}). This is why your results in row 6 are now on a different day than the original data indicates.
Also, readtable has already converted date to a datetime. No need to do this a second time.
times is created ultimately from RecHours. There is no date information here, so it doesn't make sense to use datetime to create times. It addes a meaningless date to the times. Why do this? You end up ignoring the date anyway.
Finally, you come full circle and create fullt, which appears to just be a recreation of what your 2nd line of code creates, but with a lot of intrigue and mystery behind it.
I don't see any data in 5 minute increments, so can't observe what may be happening there.
Try this updated code and let us know if the issue persists.
% Load csv file (created using Excel's Import from Image feature)
dataTable = readtable('discharge.csv');
% combine date and time to new table variable
dataTable.RecHour = hours(dataTable.RecHour/100);
dataTable.Date=dataTable.date+dataTable.RecHour
dataTable = 24×17 table
Varl DataCod Recl RecYear RecMonth Recday Watershed DayofYear RecHour Discharge Shei Corr H eight Qual date Date ____ ___________ ____ _______ ________ ______ __________ _________ _______ _________ ____ _________ _ _______ _______ ___________ ____________________ 1 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 0 hr 0.003 0 {'5...' } 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 00:00:00 2 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 3 hr 0.003 0 {'4..' } 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 03:00:00 3 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 6 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 06:00:00 4 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 9 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 09:00:00 5 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 12 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 12:00:00 6 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 15 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 15:00:00 7 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 18 hr 0.003 0 {'4...' } 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 18:00:00 8 {''ASD05''} 1 1987 1 1 {''NOIB''} 1 21 hr 0.003 0 {'4..' } 0 {''.''} {''.''} 01-Jan-1987 01-Jan-1987 21:00:00 9 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 0 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 00:00:00 10 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 3 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 03:00:00 11 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 6 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 06:00:00 12 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 9 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 09:00:00 13 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 12 hr 0.003 0 {'4...' } 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 12:00:00 14 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 15 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 15:00:00 15 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 18 hr 0.003 0 {'4....'} 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 18:00:00 16 {''ASD05''} 1 1987 1 2 {''NOIB''} 2 21 hr 0.003 0 {'4..' } 0 {''.''} {''.''} 02-Jan-1987 02-Jan-1987 21:00:00
dataTable.Date.Format = 'MM/dd/yyyy HH:mm:ss';
% Extract the desired variables to a new table
T = dataTable(:,["Date","Discharge"])
T = 24×2 table
Date Discharge ___________________ _________ 01/01/1987 00:00:00 0.003 01/01/1987 03:00:00 0.003 01/01/1987 06:00:00 0.003 01/01/1987 09:00:00 0.003 01/01/1987 12:00:00 0.003 01/01/1987 15:00:00 0.003 01/01/1987 18:00:00 0.003 01/01/1987 21:00:00 0.003 01/02/1987 00:00:00 0.003 01/02/1987 03:00:00 0.003 01/02/1987 06:00:00 0.003 01/02/1987 09:00:00 0.003 01/02/1987 12:00:00 0.003 01/02/1987 15:00:00 0.003 01/02/1987 18:00:00 0.003 01/02/1987 21:00:00 0.003
  7 个评论
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Callie
Callie 2023-11-15
Yes that works! Before I did not look at the tail and it had the wrong times. This new code works. Thank you
Peter Perkins
Peter Perkins 2023-11-16
Chris has certainly cracked that nut, but I'm gonna suggest that you use a timetable, not just a table.

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