Re: struct weirdness

[Ben Abbott]

On Aug 24, 2012, at 5:23 AM, Sergei Steshenko wrote:

> --- On Thu, 8/23/12, John W. Eaton <address@hidden> wrote:
> 
>> From: John W. Eaton <address@hidden>
>> Subject: Re: struct weirdness
>> To: "Sergei Steshenko" <address@hidden>
>> Cc: "Przemek Klosowski" <address@hidden>, "Jordi Gutiérrez Hermoso" 
>> <address@hidden>, "address@hidden" <address@hidden>
>> Date: Thursday, August 23, 2012, 3:22 PM
>> On 23-Aug-2012, Sergei Steshenko
>> wrote:
>> 
>> | "This the square brackets should be curly" - if it's a
>> must, and square brackets are accepted, then we have a bug -
>> because no error message is issued.
>> | 
>> | If square brackets are allowed, then the struct element
>> should be treated as vector in this case, which it is not -
>> see my earlier Email in the thread. So, I think, we still
>> have a bug - because square brackets are not treated as they
>> normally do.
>> 
>> It's not a bug.
>> 
>> The behavior is compatible with Matlab.
>> 
>> The [...] argument is a single Matrix object, which is a
>> single
>> "scalar" element of a cell array.  So somewhat
>> consistent with
>> handling of scalar objects in other contexts, it is
>> broadcast to all
>> dimensions of the struct array.
>> 
>> jwe
>> 
> 
> Which part of "help struct" explains that I can't apply 'size' operator to 
> something that has been specified with '[...]' ?
> 
> Thanks,
>  Sergei.

I think you're misunderstanding how structures work.  Consider "samples.age" ...

samples.age
ans =

   45   52   45   23

ans =

   45   52   45   23

ans =

   45   52   45   23

ans =

   45   52   45   23

The four "ans" are due to the samples structure having size 1x4, and is the 
same as the comma separated list (cs-list) below.

        samples(1).age, samples(2).age, samples(3).age, samples(4).age

By placing cs-list between square brackets, the entire list is collected into a 
single variable.

age = [samples.age]
age =

   45   52   45   23   45   52   45   23   45   52   45   23   45   52   45   23

size (age)
ans =

    1   16

Applying size() to [samples.age] give the expected result.

size ([samples.age])
ans =

    1   16

Entering size(samples.age) is equivalent to ...

        size (samples(1).age, samples(2).age, samples(3).age, samples(4).age)

Which isn't compatible with the syntax for the size() function.

Ben