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From: Vivek Subramanian on 27 Jul 2010 12:50
Hi everyone,

I am wondering how one can index a matrix that is returned by a function without first storing it in a variable. For instance, I am using a function called extfeature.m which returns a 1 by 45 matrix containing the values of 45 features I have extracted from an EEG signal. I would like to store only the 5th, 17th, and 38th feature values. Is there a way I can do this in one line instead of having to first initialize a variable to store all 45 values and then re-initializing it to store only those values?

In other words, I would like to do something like this:

features = (extfeature(signal))([5, 17, 38]);

rather than

features = extfeature(signal);
features = features([5, 17, 38]);

Thank you!!
Vivek
From: us on 27 Jul 2010 13:05
"Vivek Subramanian" <vas11(a)duke.edu> wrote in message <i2n2oe$3eo$1(a)fred.mathworks.com>...
> Hi everyone,
>
> I am wondering how one can index a matrix that is returned by a function without first storing it in a variable. For instance, I am using a function called extfeature.m which returns a 1 by 45 matrix containing the values of 45 features I have extracted from an EEG signal. I would like to store only the 5th, 17th, and 38th feature values. Is there a way I can do this in one line instead of having to first initialize a variable to store all 45 values and then re-initializing it to store only those values?
>
> In other words, I would like to do something like this:
>
> features = (extfeature(signal))([5, 17, 38]);
>
> rather than
>
> features = extfeature(signal);
> features = features([5, 17, 38]);
>
> Thank you!!
> Vivek

simply said: ML does NOT implement this syntax...
see the very many similar CSSM threads re this particular issue...

us
From: Walter Roberson on 27 Jul 2010 14:17
Vivek Subramanian wrote:

> I am wondering how one can index a matrix that is returned by a function
> without first storing it in a variable. For instance, I am using a
> function called extfeature.m which returns a 1 by 45 matrix containing
> the values of 45 features I have extracted from an EEG signal. I would
> like to store only the 5th, 17th, and 38th feature values. Is there a
> way I can do this in one line instead of having to first initialize a
> variable to store all 45 values and then re-initializing it to store
> only those values?

getNth = @(v,n) v(n);

getNth( extfeature(...), [5, 17, 38]);


This satisfies the letter of your requirement that you do not have to store
the value in a variable, but violates the spirit of your requirement in that
the value still gets associated with a variable which is the dummy parameter
to the anonymous function.
From: Vivek Subramanian on 29 Jul 2010 07:30
Thank you both for your responses!

Walter Roberson <roberson(a)hushmail.com> wrote in message <i2n83c$dcq$1(a)canopus.cc.umanitoba.ca>...
> Vivek Subramanian wrote:
>
> > I am wondering how one can index a matrix that is returned by a function
> > without first storing it in a variable. For instance, I am using a
> > function called extfeature.m which returns a 1 by 45 matrix containing
> > the values of 45 features I have extracted from an EEG signal. I would
> > like to store only the 5th, 17th, and 38th feature values. Is there a
> > way I can do this in one line instead of having to first initialize a
> > variable to store all 45 values and then re-initializing it to store
> > only those values?
>
> getNth = @(v,n) v(n);
>
> getNth( extfeature(...), [5, 17, 38]);
>
>
> This satisfies the letter of your requirement that you do not have to store
> the value in a variable, but violates the spirit of your requirement in that
> the value still gets associated with a variable which is the dummy parameter
> to the anonymous function.
From: Matt J on 29 Jul 2010 10:47
"Vivek Subramanian" <vas11(a)duke.edu> wrote in message <i2n2oe$3eo$1(a)fred.mathworks.com>...
> Hi everyone,
>
> I am wondering how one can index a matrix that is returned by a function without first storing it in a variable. For instance, I am using a function called extfeature.m which returns a 1 by 45 matrix containing the values of 45 features I have extracted from an EEG signal. I would like to store only the 5th, 17th, and 38th feature values. Is there a way I can do this in one line instead of having to first initialize a variable to store all 45 values and then re-initializing it to store only those values?
==========

Yes, you can use the following FEX tool

http://www.mathworks.com/matlabcentral/fileexchange/26570-direct-indexing-of-function-calls-oop-exercise

It would allow you to do something like this

%Get an indexable function handle to extfeature
>> h=IndexableFunction(extfeature);

%Call extfeature with arg1,arg2,etc... and index result at 5th,17th,18th elements
>> result=h{arg1,arg2,...}([5,17,38])
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