How do I calculate the daily average for a large data set?

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Rodney Dwyer 2016-1-19

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评论： mdi 2018-8-1

I have stored the date in variable with year, month, day, hour, minute, and second. I have a another vector with significant wave height with the same number of rows. However, it is possible for days to have different numbers of data points. I would like to produce a plot with the day of the month and the average of the significant wave height for each day within the set. In Excel, I can use a pivot table. How do I perform the same function in Matlab?

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Answer 1

the cyclist 2016-1-20

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You should be able to use the accumarray function.

If you upload your data (or a representative segment of it), someone here could give you some more specific advice on how to use it.

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Rodney Dwyer 2016-1-20

Test.xlsx

the cyclist thank you for your response. Here is a short sample of the spread sheet that has the rows and columns I need. Ideally I would like to get a daily average for the significant wave height and a daily max for the the max height.

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Answer 2

the cyclist 2016-1-21

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在 MATLAB Online 中打开

You need to do three things:

Import the data
Convert your y/m/d columns into their unique datenums (which you can do with the datenum command)
Get the daily mean (which you can do with accumarray)

Here is a code snippet that shows you how to do the last step:

% List of your date numbers
dateList = [736350; 736350; 736350; 736351; 736351; 736352; 736352; 736352];
% Corresponding values
value      = [     1;      2;      3;      4;      5;      6;      7;      8];
% Get the unique dates, and their indices
[uniqueDays,idxToUnique,idxFromUniqueBackToAll] = unique(dateList);
dailyMean = accumarray(idxFromUniqueBackToAll,value,[],@mean);

If you can't figure out the other two steps, perhaps post another question.

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mdi 2018-8-1

hi there, I was looking to do so and couldn`t figure out the last two steps, can you elaborate, please? and in addition, can you please in which time format I should load the data? for now all my data are stored in .csv files in the general format.

thanks in advance

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