Re: structure array equivalent in Mathematica
- To: mathgroup at smc.vnet.net
- Subject: [mg67229] Re: structure array equivalent in Mathematica
- From: Rolf.Mertig at gmail.com
- Date: Tue, 13 Jun 2006 01:07:30 -0400 (EDT)
- References: <e6gdun$ngj$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Here are two possibilities to do what you want:
(* by using a datatype identitifier the order of data can be arbitrary:
*)
observation = {
DataType["pressure"][10.], DataType["temperature"][20.],
DataType["water_vapor"][30.]
}
(* one possibility to define the "method" - functions : *)
pressure =
Function[x,Cases[x,DataType["pressure"][_?NumberQ],-1]/.DataType[_][y_]:>y/.{z_}:>z];
temperature =
Function[x,Cases[x,DataType["temperature"][_?NumberQ],-1]/.DataType[_][y_]:>y/.{z_}:>z];
watervapor =
Function[x,Cases[x,DataType["water_vapor"][_?NumberQ],-1]/.DataType[_][y_]:>y/.{z_}:>z];
{
pressure @ observation
,
temperature @ observation
,
watervapor @ observation
}
data["obs_day"] = {observation, observation, observation};
pressure @ data["obs_day"][[1]]
(* this will also work, by design: *)
pressure @ data["obs_day"]
(* ********************** *)
(* for a lot of data it is more efficient to represent the different
data types by position only: *)
observation2 = {10., 20., 30.};
{
pressure2 = Function[obs, obs[[1]]];
,
temperature2 = Function[obs, obs[[2]]];
,
watervapor2 = Function[obs, obs[[3]]];
}
pressure2 @ observation2
temperature2 @ observation2
watervapor2 @ observation2
data2["obs_day"] = {observation2, observation2, observation2};
pressure2 @ data2["obs_day"][[1]]
---
Regards,
Rolf Mertig
http://www.gluonvision.com
GluonVision GmbH
Berlin
kevin_jazz wrote:
> Like many people I imagine, I'm transitioning to Mathematica from a
> background in another system.
> One of the common data types is the structure array. Let's say I have
> an observational data set that includes pressure, temperature, and
> water vapor as a function of altitude. So, in pseudo-code I might
> define a structure as
>
> observation = {pressure: float(100), temperature: float(100),
> water_vapor: float(100)}
>
> I could then access the elements of this observation as
>
> observation.pressure
> observation.temperature, etc.
>
> Furthermore, I could aggregate these observations into a larger list, e.g.
> obs_day = {observation, observation, observation}
> to be accessed as
> obs_day[1].pressure for the first element (assuming 1-index).
>
> Now, the list in Mathematica is quite powerful and I think can be
> set-up in a similar fashion.
>
> So my question is how is the structure array commonly implemented in
> Mathematica or its equivalent?
>
> If there is a previous thread (I looked but didn't find any) on the
> topic or in the Mathematica book or Mathematica Journal that I missed,
> feel free to point me in that direction.
>
> Many thanks,
>
> Kevin Bowman
> Jet Propulsion Laboratory