how to convert hourly average into monthly??

Question

SD 2018-3-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/390139-how-to-convert-hourly-average-into-monthly

回答： Razvan Carbunescu 2018-4-1

采纳的回答： Pawel Jastrzebski

在 MATLAB Online 中打开

i have data for hourly. i need the monthly average of the each hour of the day.

eg: date time data

     01/03/18   1:00:00     2.365
     02/03/18   1:00:00     3.235
     03/03/18   1:00:00     10.2655
     ..............
     ..............
     29/03/18   1:00:00     45.6552
     30/03/18   1:00:00     32.2552
     31/03/18   1:00:00     15.3565
in this way i need all 24 hours average for a month. 
this kind of data is for  4 years. 
is there any possible program related to this problem,
if anyone can solve thanks in advance.
this is the data available with me.
but as i mentioned above i need the average of the each hour of the month.
i.e, 01/01/2012 1:00:00+02/01/2012 1:00:00+......31/01/2012 1:00:00.
like this 24 hours for a month and 12 months for a year.

i want to do mean of the first hour values of a month,then second hour values for amonth and so on last hour i.e,23 rd hour mean for a month. i hope you understood my problem,if not i will explain you clearly one more time.

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SD 2018-3-23

this is the data available with me.but as i mentioned above i need the average of the each hour of the month.i.e, 01/01/2012 1:00:00+02/01/2012 1:00:00+......31/01/2012 1:00:00.like this 24 hours for a month and 12 months for a year.

i want to do mean of the first hour values of a month,then second hour values for amonth and so on last hour i.e,23 rd hour mean for a month. i hope you understood my problem,if not i will explain you clearly one more time.

dpb 2018-3-23

编辑：dpb 2018-3-23

Attach the data itself (representative sample) instead of image; we can't do anything with that.

See <splitapply> for how to group data, though, should get you going.

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Answer 1

Pawel Jastrzebski 2018-3-23

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/390139-how-to-convert-hourly-average-into-monthly#answer_311543

在 MATLAB Online 中打开

Use the logical vectors for conditioning your data as in the example below. You'll need some loops to go over every hour:

% example data
% date generation
t1 = datetime(2018,01,01,0,0,0);
t2 = datetime(2018,03,31,0,0,0);
t = (t1:hours(1):t2)';
% hourly value generation
hourlyVal = randi(10,length(t),1);
% store all in a table
T = table(t,hourlyVal)
%---CALCULATE---
% average for hour 00:00 in January 2018
% CONDITION
condition = ...
    year(T.t) == 2018 & month(T.t) == 1 & hour(T.t) == 0;
% VALUE
aveJan18_00 = mean(T.hourlyVal(condition))

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Pawel Jastrzebski 2018-3-27

在 MATLAB Online 中打开

How do you store your data in MATALB? Is it in a table?

If so you will access your data using the actual variables:

 aveJan18_00 = mean(...
    TableName.VariableName(condition))

If you imported the table and no name was assigned to its variables (columns), it will hold a generic names for the variables:

Then your code would look more like this:

aveJan18_00 = mean(...
   TableName.Var3(condition))

Or alternatively, use column indexing to access i.e. column no 3. More on that:

Access Data in a Table

---

The example I have provided earlier was a quick fix - but the example was to show you how you can use vectors to extract the data from you set and calculate the average. Naturally, it requires some work on your side to understand the example and improve the code so it is more efficient. I'm not claiming this is the most efficient way, but I disagree with dpd 's statement that this is not the Matlab way.

To expand on my example, I've created a table of conditions, to show you that you:

Can collect all of your conditions in one place
Use only one loop to carry out the calculation
Don't need to create a new variable for every average you want to calculate

% EXAMPLE DATA
% date generation
t1 = datetime(2017,010,01,0,0,0);
t2 = datetime(2018,03,31,0,0,0);
t = (t1:hours(1):t2)';
% random hourly value generation
hourlyVal = randi(10,length(t),1);
% store all in a table
T = table(t,hourlyVal)
clear t1 t2 t hourlyVal;
% CREATE CONDITIONS TO CHECK
% Create a list of of all of the conditions for you to check
% And store them in a table for convenience
y = (2017:2018)'; % year span
m = (1:12)';
h = (0:23)';
h1 = repmat(h,numel(m)*numel(y),1);
m1 = repelem(m,numel(h));
m1 = repmat(m1,numel(y),1);
y1 = repelem(y,numel(m)*numel(h));
% create table of the 'date' condtions to check
T_cond = table(y1, m1, h1);
% add column for the average that will be calculated from the data
T_cond.Ave(:) = 0;
clear y m h y1 h1 m1;
% CALCULATE AND STORE THE REQUIRED AVERAGE 
% One loop to go over evry condition from 'T_cond'
% And if the condition is met, evaluate the avetage for the DATA
for i = 1:size(T_cond,1)
      condition  = ...
      year(T.t)  == T_cond.y1(i) & ...
      month(T.t) == T_cond.m1(i) & ...
      hour(T.t)  == T_cond.h1(i);
      T_cond.Ave(i) = mean(T.hourlyVal(condition));
end

In this example you'll see that:

Your fake date span ranges from 10.2017 to 03.2018
Conditions to calculate the average for are created easily with this code:

y = (2017:2018)'; % year span
m = (1:12)';
h = (0:23)';
h1 = repmat(h,numel(m)*numel(y),1);
m1 = repelem(m,numel(h));
m1 = repmat(m1,numel(y),1);
y1 = repelem(y,numel(m)*numel(h));
% create table of the 'date' condtions to check
T_cond = table(y1, m1, h1);

Lastly, code calculates the average where data is available and conditions are met:

Last thoughts:

Yes, Matlab philosophy is not to use loops if you don't have to
But at the same time it's not a crime to use them, use whatever method and programming skills you're comfortable with
There's always room for improvement