How can i compute the mean of specific number of table rows?

Hi, I have a large amount of table data which is divided by date and time....to be more specific i have data that is per 10 minutes and i want to compute the mean of them per hour! In other words, i want ot compute the mean of my data per 10 rows until my data is finished! Is this possible and if yes....which command should i use?

Answer 1

[Cong Ba]

Try reshape:

a = randn(100,1);  % assume this is the column you have

b = reshape(a,[10,10]); % reshape it so each column has 10 rows

avg = mean(b);

[Ioannis Tsikriteas]

Can yoy please explain to me the meaning of those commands. Excuse me but i am a beginner at Matlab

P.S: My table is 278984x2 with data per 10 minutes which i want to transform to data per 1 hour so i want to compute the mean per 6 rows!

[Cong Ba]

let's assume you throw the first 2 rows...

a = randn(278984,2);  % assume this is your table
a = a(3:end,:); % assme throw out the first two rows
b1 = reshape(a(:,1),[6, 278982/6]); % reshape the first column to [6, 278982/6] so it has 6 rows
avg1 = mean(b1);
b2 = reshape(a(:,2),[6, 278982/6]); % same to the second column
avg2 = mean(b2);

avg1 would be the hourly series you want for the first column of your data. avg2 would be for the second.

[Ioannis Tsikriteas]

When i try the reshape command i get the following message: Error using tabular/reshape (line 150) Undefined function 'reshape' for input arguments of type 'table'.

To be more clear isend a pic of the shape of my data tables

[Cong Ba]

Andrei is using the timetable function which may better suit your need (you essentially have a time series). But if you want to manipulate data in matrix form (my code works for matrix form), you can try this function: table2array

Answer 2

[Andrei Bobrov]

n = 278984;
t = minutes(10*(1:n)');
D = randi(255,n,2); % Let D - your data (278984 x 2)

TT = timetable(t,D(:,1),D(:,2));
TT_out = retime(TT,'hourly','mean');

[Ioannis Tsikriteas]

I am sorry but i didn't understand the concept of these commands.

Mine data are already ona a table 278984x2 and has the following shape:

I am searching a way to compute the mean between the fifth and the eleventh row for example in order to have my data per hour, not per 10 minutes

[Andrei Bobrov]

a.x_10_double = [a.x_10_{:}]';
TT = table2timetable(a(:,[1,3]),'RowTimes','x08_Jul_100_10_00');
TT_out = retime(TT,'hourly','mean');

or

a2 = table(a{:,1},[a{:,2}{:}]','v',{'datetime','x_10_double'})
a2.groups = hour(a2{:,1});
a_out = varfun(@mean,a2,'Group','groups');

Answer 3

[Peter Perkins]

Add a grouping variable to your table and use varfun. Something like

n = ceil(height(t)/10);
g = repelem(1:n,10)';
t.Group = g(1:height(t));
t.groupMeans = varfun(@mean,t,'GroupingVariable','Group')