Time Series analysis problems with date

2021 1 4
1 个回答
更新时间：2022 1 25
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Hi all-and a happy new year (lets hope its better than the last one......)
My query concerns time series.
I have a dataset which consists of 7 seperate excel files, first column is date and second column is a scalar number.
The date is a period of 8 months, jan-aug for 10 years (repeated in each excel file).
I have plotted the first file and the first 8 months plot fine for the ten year period, however, the sep-dec period is also plotted which shows no data, therefore there is a straight line until the next year starts on the graph.
I have used the code
= datevec(cam{:,1}); and also tried
= datenum (cam{:,1});
both do not work!!
So my question is how do I plot the data for just the dates shown which Jan 1st-Aug 31st 2010-2020?
Im fairly new to all this, I have tried using the mathworks help section and tried several other pieces of code, but I get the dreaded red writing, I apologise if this is a billy basic question!
many thanks in advance
Mike

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Eric Sofen
Eric Sofen 2021-1-6
It will be helpful to see some sample data and more of the code you've tried to write for context. I'm not sure what cam{:,1} refers to.
To get things started, I'd encourage you to use the datetime type rather than the older datenum/datevec.
mike
mike 2021-1-16
Hey Eric,
sorry for the delay in response!
Column 1 are the dates and column 2 are the values I am interested in.
% this is how I load the data
infmt = 'dd-MM-yyyy';
data_all = datetime(testData{:,1}, 'InputFormat',infmt);
gas = testData{:,2};
I now tried to replace the values from Sep-Dec with NaN, but this tricks Matlab into thinking that these values are equal to dates where there are no measurements (eg system failure). So I can't do interpolation etc.
I then tried to concatenate (see below), but this somehow looses all the date information.
n2010 = find(data_all>='2010-01-01' & data_all<='2010-08-31');
n2011 = find(data_all>='2011-01-01' & data_all<='2011-08-31');
C1=cat(1,n2010,n2011);
Is there a way to only select/plot Jan-Aug over a set period of years?
Thank you!
Adam Danz
Adam Danz 2021-1-17
Is the goal to remove the straight line from the data while maintaining the sept-dec dates along the x axis? Or is the goal to remove the gap completly and jump from Aug to Jan along the x axis?
mike
mike 2021-1-17
Hi Adam,
Ideally to remove the lines and the gaps from the x axis so that I can them smooth and detrend.
Cheers

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回答（1 个）

Biral Pradhan
Biral Pradhan 2022-1-25

0 个投票

I understand, you want to remove the straight line as well as x-axis labels corresponding to those 4 months (Sep-Dec) for each year. I assume, you plan on interpolating the data for these 4 months later. While plotting monthly data using datetime values from different tables (as in your case), the axis spacing is determined uniformly, so you get labels separated by 1 calendar month.
I do not think it is possible to abruptly change the spacing from 1 calender month to 4 abruptly. A workaround would be to use a timetable and resample your data.

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mike
mike
2021-1-4

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Biral Pradhan
Biral Pradhan
2022-1-25

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