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Matt
Posts:
513
Registered:
7/22/07


Re: Labelbased addressing
Posted:
Apr 9, 2013 3:04 PM


kj <no.email@please.post> wrote in message <kjvig1$1i9$1@reader1.panix.com>... > > > > Let me start with a hypothetical (but representative) usecase. > 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 kvector of > statistics (e.g. total consumption, consumption per capita, etc.). > Therefore, all told, I'm talking about a fourdimensional > (5 x 8 x 4 x 50) array of kvectors. > > 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, > labelbased addressing would allow me to use something like > > E = D.extract(state="AK", age="3045") > > 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 ndimensional "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/39336datasetobject
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



