Re: [Pytables-users] Tables vs Arrays

[Francesc A. <fa...@gm...>]

On 7/28/13 9:58 PM, Anthony Scopatz wrote:
>
> On Sun, Jul 28, 2013 at 8:38 PM, David Reed <dav...@gm... 
> <mailto:dav...@gm...>> wrote:
>
>     I'm really trying to become more productive using PyTables, but am
>     struggling with what I should be using.  Whats the difference
>     between a table and an array?
>
>
> Hi David,
>
> The difference between Arrays and Tables, conceptually is the same as 
> the different between numpy arrays and numpy structured arrays.  The 
> plain old [Aa]rray is a continuous block of a single data type. 
>  Tables and structured arrays have a more complex data type that is 
> composed of a continuous sequence of other data types (ie the fields / 
> columns).  Which data structure you use really depends a lot of the 
> type of problem you are trying to solve and what kinds of questions 
> you want to answer with that data structure.
>
> That said, the implementation of Tables is far more similar to EArrays 
> than Arrays.  So a lot of the performance trade offs that you see are 
> similar.

Besides this, another interesting difference is that Tables allow 
queries to be performed in a similar way to relational databases (but 
using a more NumPy-esque syntax).  Here it is some examples:

http://pytables.github.io/cookbook/hints_for_sql_users.html?highlight=query#selecting-data

and you can index columns too:

http://pytables.github.io/cookbook/hints_for_sql_users.html?highlight=query#creating-an-index

so that you can accelerate queries involving indexed columns.

-- 
Francesc Alted