Thread Subject: Dynamic Fields

Hi

I currently have a 1x1 sturcture. The structure contains
6001x3 array.

s=load('Patient1_PV_PEEP1.mat'
J = fieldnames(s)
n1=500;
n2=35/0.01;
t=s.(J)(n1:n2,1)
P=s.v(n1:n2,2)
V=s.v(n1:n2,3)

The code loads up the mat file. This may change depending
on the patient. Three variables in the array are time,
pressure and volume. The name of the field is
Patient1_PV_PEEP1 and this is variable depending on
patient. When I attempt to use dynamic field names, the
lines with t, P and V give me this message:

'Argument to dynamic structure reference must evaluate to a
valid field name'

Cheers

"Ashwath Sundaresan" <asu33@student.canterbury.ac.nz> wrote in message
news:fqif1a$dbo$1@fred.mathworks.com...
> Hi
>
> I currently have a 1x1 sturcture. The structure contains
> 6001x3 array.
>
> s=load('Patient1_PV_PEEP1.mat'
> J = fieldnames(s)
> n1=500;
> n2=35/0.01;
> t=s.(J)(n1:n2,1)
> P=s.v(n1:n2,2)
> V=s.v(n1:n2,3)
>
> The code loads up the mat file. This may change depending
> on the patient. Three variables in the array are time,
> pressure and volume. The name of the field is
> Patient1_PV_PEEP1 and this is variable depending on
> patient. When I attempt to use dynamic field names, the
> lines with t, P and V give me this message:
>
> 'Argument to dynamic structure reference must evaluate to a
> valid field name'

From the reference page:

http://www.mathworks.com/access/helpdesk/help/techdoc/ref/fieldnames.html

"names = fieldnames(s) returns a cell array of strings containing the
structure field names associated with the structure s."

A cell array of strings is not a valid field name. A valid field name is a
string (technically, a 1-by-N char array) that satisfies the criteria listed
in the M-file help for the ISVARNAME function.

Try "t = s.(J{1})(n1:n2, 1)"

--
Steve Lord
slord@mathworks.com

"Ashwath Sundaresan" <asu33@student.canterbury.ac.nz> wrote
in message <fqif1a$dbo$1@fred.mathworks.com>...
> Hi
>
> I currently have a 1x1 sturcture. The structure contains
> 6001x3 array.
>
> s=load('Patient1_PV_PEEP1.mat'
> J = fieldnames(s)
> n1=500;
> n2=35/0.01;
> t=s.(J)(n1:n2,1)
> P=s.v(n1:n2,2)
> V=s.v(n1:n2,3)
>
> The code loads up the mat file. This may change depending
> on the patient. Three variables in the array are time,
> pressure and volume. The name of the field is
> Patient1_PV_PEEP1 and this is variable depending on
> patient. When I attempt to use dynamic field names, the
> lines with t, P and V give me this message:
>
> 'Argument to dynamic structure reference must evaluate to
a
> valid field name'
>
> Cheers
>

J is that a character string or a cell array (1x1) of
strings? Should be the former / per