Prev: in-place operations in matlab
Next: creating a list of dates from file names
From: Evan on 25 Jul 2010 15:38
I can't seem to figure out how to find the mean of the non-zero elements in the rows of a 2-D array without using a for loop..

Suppose I have a 2D array

Bob =
0 50 54 0
0 50 52 0
0 52 54 0
0 58 60 0

Is there an easy way to find the mean of each row while keeping the result a 2D array like:

Result: 52
51
53
59

I've tried the nonzeros command, but it keeps flattening the array before the mean command and I get the mean of the whole array rather than a row at a time. Is there some simple way to do this without using a for loop to parse through each row at a time?

Thanks!
From: us on 25 Jul 2010 15:46
"Evan " <Evan(a)fake.com> wrote in message <i2i3qr$lb8$1(a)fred.mathworks.com>...
> I can't seem to figure out how to find the mean of the non-zero elements in the rows of a 2-D array without using a for loop..
>
> Suppose I have a 2D array
>
> Bob =
> 0 50 54 0
> 0 50 52 0
> 0 52 54 0
> 0 58 60 0
>
> Is there an easy way to find the mean of each row while keeping the result a 2D array like:
>
> Result: 52
> 51
> 53
> 59
>
> I've tried the nonzeros command, but it keeps flattening the array before the mean command and I get the mean of the whole array rather than a row at a time. Is there some simple way to do this without using a for loop to parse through each row at a time?
>
> Thanks!

one of the many solutions
- for this particular case...

m=[
0 50 54 0
0 50 52 0
0 52 54 0
0 58 60 0
];
r=mean(m(:,2:3),2)
%{
% r =
52
51
53
59
%}

us
From: Roger Stafford on 25 Jul 2010 15:53
"Evan " <Evan(a)fake.com> wrote in message <i2i3qr$lb8$1(a)fred.mathworks.com>...
> I can't seem to figure out how to find the mean of the non-zero elements in the rows of a 2-D array without using a for loop..
>
> Suppose I have a 2D array
>
> Bob =
> 0 50 54 0
> 0 50 52 0
> 0 52 54 0
> 0 58 60 0
>
> Is there an easy way to find the mean of each row while keeping the result a 2D array like:
>
> Result: 52
> 51
> 53
> 59
>
> I've tried the nonzeros command, but it keeps flattening the array before the mean command and I get the mean of the whole array rather than a row at a time. Is there some simple way to do this without using a for loop to parse through each row at a time?
>
> Thanks!
- - - - - - - - -
Use the nanmean function of the Statistics toolbox.

Roger Stafford
From: Roger Stafford on 25 Jul 2010 15:55
What I meant to say was convert the zeros to NaNs and then use nanmean.

Roger Stafford
From: Roger Stafford on 25 Jul 2010 16:03
"Evan " <Evan(a)fake.com> wrote in message <i2i3qr$lb8$1(a)fred.mathworks.com>...
> I can't seem to figure out how to find the mean of the non-zero elements in the rows of a 2-D array without using a for loop..
>
> Suppose I have a 2D array
>
> Bob =
> 0 50 54 0
> 0 50 52 0
> 0 52 54 0
> 0 58 60 0
>
> Is there an easy way to find the mean of each row while keeping the result a 2D array like:
>
> Result: 52
> 51
> 53
> 59
>
> I've tried the nonzeros command, but it keeps flattening the array before the mean command and I get the mean of the whole array rather than a row at a time. Is there some simple way to do this without using a for loop to parse through each row at a time?
>
> Thanks!
- - - - - - - -
Without the statistics toolbox you can use

sum(m(m~=0),2)./sum(m~=0,2)

Roger Stafford
 |  Next  |  Last
Pages: 1 2 3
Prev: in-place operations in matlab
Next: creating a list of dates from file names