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Topic: Label-based addressing
Replies: 4   Last Post: Apr 9, 2013 3:04 PM

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Matt

Posts: 513
Registered: 7/22/07
Re: Label-based addressing
Posted: Apr 9, 2013 3:04 PM
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kj <no.email@please.post> wrote in message <kjvig1$1i9$1@reader1.panix.com>...
>
>
>
> Let me start with a hypothetical (but representative) use-case.
> Suppose I have data stratified over 5 brands of beer, 8 yearly
> quarters, 4 age groups, and 50 states. Furthermore, let's say that
> for each possible combination of beer brand, yearly quarter, age
> group, and state, I have computed a heterogenous k-vector of
> statistics (e.g. total consumption, consumption per capita, etc.).
> Therefore, all told, I'm talking about a four-dimensional
> (5 x 8 x 4 x 50) array of k-vectors.
>
> I would like to store all this data in an object that would allow
> me to address subsets of it using *labels* instead of numeric
> indices. By "labels" I mean the names of the "dimensions" (in this
> case "brand", "quarter", "age", "state"), the names of the possible
> values for each dimension, (e.g. for state, I'd have "AK", "AL",
> "AR", ..., "WI", "WY"), and the components of the vector of data
> associated with each combination of factors, (in this case these
> would include "total consumption", "consumption per capita", etc.).
>
> For example, supposing that the variable D held such a data structure,
> label-based addressing would allow me to use something like
>
> E = D.extract(state="AK", age="30-45")
>
> to store in E the subset of the data in D corresponding to the
> specified values. (The value in E, by the way, would be a similar
> data structure, but it would have different shape, since two of
> its dimensions now have the minimum depth of 1.)
>
> One can imagine many elaborations of this theme, but I think the
> above gives a flavor of what I have in mind.
>
> It is my understanding that MATLAB does not have this functionality.
> (But please correct me if I'm wrong!) Therefore I'd have to
> implement it myself.
>
> My naive idea is to define an object (class, that is) that internally
> stores one or more n-dimensional "boxes" for the data (as standard
> MATLAB arrays), as well as hash tables to map between labels and
> numeric indices. Methods like "extract" above would convert its
> arguments to numeric addresses, and would use these numeric addresses
> to fetch the data from the internal data boxes.
>
> I am fairly new to MATLAB, so I'd appreciate your comments on the
> above, and any words of wisdom you may give me on how best to do
> this.
>
> In particular, are there any existing packages I could use as
> *models* for this sort of project?
>
> Thanks in advance!
>
> kj


Hi KJ -

Not sure it does exactly what you want but you might take a look at the DataSet Object I put on the file exchange a few months ago:

http://www.mathworks.com/matlabcentral/fileexchange/39336-dataset-object

It allows index into data via label names. For example:

myds = dataset(rand(5,5,3));%Create a dataset.
%Add different formatted labels.
myds.label{1,1} = str2cell(sprintf('Row_%d\n',[1:5]'));%Add labels to mode 1.
myds.label{2,1} = str2cell(sprintf('Column %d\n',[1:5]'));%Add labels to mode 2.
myds.label{3,1} = str2cell(sprintf('Slab%d\n',[1:3]'));%Add labels to mode 3.

myslab = myds.Slab1;%Get first "slab" of the cube (5x5x1).
mycol = myds.Slab1.('Column 1');%Get first column from cube (5x1x1).


Scott



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