MATLAB Central Newsreader - Data Bin

Data Bin

AP Pal — Sun, 04 Oct 2009 15:43:01 -0400

I am new to matlab and am stuck with what seems simple task
i have a column of data 1000 pts long. i need to average in groups of 10 so i need to generate a new matrix which has 100pts.

i was trying to write a code with a mini file and keep making mistakes

p=X
n=1;
i=1;
m=length(X);

avg_pts= 2;
z= length(X)/avg_pts
% q=0;
p(1,1)=X(1,1);

  for i=(1:1:z);

       for q=(1:1:avg_pts);
           if n+q<=m
       p(q,1)=p(q,1)+X(n+q,1);
           else
           end
       end
       y(i,1)=p(q,1)/avg_pts;
      n=n+avg_pts;

  end

Any help will be greatly appreciated
thanks

Re: Data Bin

Andrew Stevens — Sun, 04 Oct 2009 17:05:03 -0400

"AP Pal" <avispal@gmail.com> wrote in message <haafq5$mvs$1@fred.mathworks.com>...
> I am new to matlab and am stuck with what seems simple task
> i have a column of data 1000 pts long. i need to average in groups of 10 so i need to generate a new matrix which has 100pts.
>
> i was trying to write a code with a mini file and keep making mistakes
>
> p=X
> n=1;
> i=1;
> m=length(X);
>
> avg_pts= 2;
> z= length(X)/avg_pts
> % q=0;
> p(1,1)=X(1,1);
>
> for i=(1:1:z);
>
> for q=(1:1:avg_pts);
> if n+q<=m
> p(q,1)=p(q,1)+X(n+q,1);
> else
> end
> end
> y(i,1)=p(q,1)/avg_pts;
> n=n+avg_pts;
>
> end
>
>
> Any help will be greatly appreciated
> thanks

Hi,

You many want to try something like:

%generate a dataset
y=rand(1000,1);

%average in 10 point bins
ym=mean(reshape(y,10,100));

-Andrew

Re: Data Bin

AP Pal — Sun, 04 Oct 2009 19:15:03 -0400

Thanks a lot Andrew, it really saved me so much headache.

"Andrew Stevens" <astevens@JUNKusgs.gov> wrote in message <haakjv$6r1$1@fred.mathworks.com>...
> "AP Pal" <avispal@gmail.com> wrote in message <haafq5$mvs$1@fred.mathworks.com>...
> > I am new to matlab and am stuck with what seems simple task
> > i have a column of data 1000 pts long. i need to average in groups of 10 so i need to generate a new matrix which has 100pts.
> >
> > i was trying to write a code with a mini file and keep making mistakes
> >
> > p=X
> > n=1;
> > i=1;
> > m=length(X);
> >
> > avg_pts= 2;
> > z= length(X)/avg_pts
> > % q=0;
> > p(1,1)=X(1,1);
> >
> > for i=(1:1:z);
> >
> > for q=(1:1:avg_pts);
> > if n+q<=m
> > p(q,1)=p(q,1)+X(n+q,1);
> > else
> > end
> > end
> > y(i,1)=p(q,1)/avg_pts;
> > n=n+avg_pts;
> >
> > end
> >
> >
> > Any help will be greatly appreciated
> > thanks
>
> Hi,
>
> You many want to try something like:
>
> %generate a dataset
> y=rand(1000,1);
>
> %average in 10 point bins
> ym=mean(reshape(y,10,100));
>
> -Andrew

Re: Data Bin

AP Pal — Mon, 05 Oct 2009 16:49:03 -0400

Any fast way to reshape the whole matrix?
i mean converting from 100X 50
to 10X 50

by averaging the 10 rows at a time to bin

the reshape funtion worked for n X 1 matrix only.

"AP Pal" <avispal@gmail.com> wrote in message <haafq5$mvs$1@fred.mathworks.com>...
> I am new to matlab and am stuck with what seems simple task
> i have a column of data 1000 pts long. i need to average in groups of 10 so i need to generate a new matrix which has 100pts.
>
> i was trying to write a code with a mini file and keep making mistakes
>
> p=X
> n=1;
> i=1;
> m=length(X);
>
> avg_pts= 2;
> z= length(X)/avg_pts
> % q=0;
> p(1,1)=X(1,1);
>
> for i=(1:1:z);
>
> for q=(1:1:avg_pts);
> if n+q<=m
> p(q,1)=p(q,1)+X(n+q,1);
> else
> end
> end
> y(i,1)=p(q,1)/avg_pts;
> n=n+avg_pts;
>
> end
>
>
> Any help will be greatly appreciated
> thanks

Re: Data Bin

AP Pal — Mon, 05 Oct 2009 16:49:03 -0400

Re: Data Bin

Jan Simon — Mon, 05 Oct 2009 20:01:20 -0400

Dear AP Pal!

> Any fast way to reshape the whole matrix?
> i mean converting from 100X 50
> to 10X 50
>
> by averaging the 10 rows at a time to bin
>
> the reshape funtion worked for n X 1 matrix only.

No, RESHAPE works really fast for any array, not just for [n x 1] matrices!

The mentioned solution is efficient. A little bit faster, because it avoids the overhead of calling the function MEAN:
X = rand(100, 50);
Y = sum(reshape(X, 10, 10, 50), 1) / 10;

Kind regards, Jan

Re: Data Bin

AP Pal — Mon, 05 Oct 2009 22:12:03 -0400

Thanks a lot Jan .. you rock!!
now only if some one answers in my other thread to add listbox i will be set( for the time being) :P

"Jan Simon" <matlab.THIS_YEAR@nMINUSsimon.de> wrote in message <hadjaf$pn1$1@fred.mathworks.com>...
> Dear AP Pal!
>
> > Any fast way to reshape the whole matrix?
> > i mean converting from 100X 50
> > to 10X 50
> >
> > by averaging the 10 rows at a time to bin
> >
> > the reshape funtion worked for n X 1 matrix only.
>
> No, RESHAPE works really fast for any array, not just for [n x 1] matrices!
>
> The mentioned solution is efficient. A little bit faster, because it avoids the overhead of calling the function MEAN:
> X = rand(100, 50);
> Y = sum(reshape(X, 10, 10, 50), 1) / 10;
>
> Kind regards, Jan

Re: Data Bin

Jos — Tue, 06 Oct 2009 09:05:06 -0400

"Jan Simon" <matlab.THIS_YEAR@nMINUSsimon.de> wrote in message <hadjaf$pn1$1@fred.mathworks.com>...
> Dear AP Pal!
>
> > Any fast way to reshape the whole matrix?
> > i mean converting from 100X 50
> > to 10X 50
> >
> > by averaging the 10 rows at a time to bin
> >
> > the reshape funtion worked for n X 1 matrix only.
>
> No, RESHAPE works really fast for any array, not just for [n x 1] matrices!
>
> The mentioned solution is efficient. A little bit faster, because it avoids the overhead of calling the function MEAN:
> X = rand(100, 50);
> Y = sum(reshape(X, 10, 10, 50), 1) / 10;
>
> Kind regards, Jan

If the number of elements is not a multiple of the number you want to average over, you can use ACCUMARRAY

A = 1:8
n = 3 ;

% M = sum(reshape(A,n,[]))/10 % fails !!
idx = 1:numel(A)
groupnr = ceil(idx / n)
M = accumarray(groupnr(:),A(:),[],@mean)
% or in 1 step,
% M = accumarray(ceil((1:numel(A))/n).',A.',[],@mean)

Jos