[Numpy-discussion] Selection of only a certain number of fields

Neil neilcrighton@gmail....
Sun Feb 8 10:09:02 CST 2009


Francesc Alted <faltet <at> pytables.org> writes:

> > What are some common use cases for this feature?
> >
> > I use structured arrays quite a lot, but I haven't found myself
> > wanting something like this. If I do need a subset of a structured
> > array generally I use something like
> >
> > [rec[n] for n in 'name age gender'.split()]
> 
> Good point.  However, there are still some very valid reasons for having 
> an idiom like:
> 
> newarr = arr[['name', 'age']]
> 
> returning a record array.
> 
> The first one (and most important IMO), is that newarr continues to be 
> an structured array (BTW, when changed this name from the original 
> record array?), and you can use all the features of these beasts with 
> it.  Other reason (albeit a bit secondary) is that its data buffer can 
> be shared through the array interface with other applications, or plain 
> C code, in a relatively straightforward way.  However, if newarr 
> becomes a list (or dictionary), this is simply not possible.
> 
> Cheers,
> 

That's not a sample use case ;)

One of the things I love about Python is that it has a small core set of
features and tries to avoid having many ways to do the same thing.  This makes
it extremely easy to learn.  With every new feature, numpy gets a little bit
harder to learn, there's more to document and the code base gets larger and so
harder to maintain.  In those senses, whenever you add a new function/feature to
numpy, it gets a little bit worse.

So I think it would be nice to have some concrete examples of what the new
feature will be useful for, just to show how it outweighs those negatives.  As a
bonus, they'd provide nice examples to put in the documentation :).

Neil

PS.  Thanks for your work on pytables!  I've used it quite a bit, mostly for
reading hdf5 files.




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