Thread: [Pytables-users] Tables vs Arrays

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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?

On Sun, Jul 28, 2013 at 8:38 PM, David Reed <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.

You should watch my "HDF5 is for Lovers" talk for more generic advice [1].
 I hope this helps!

Be Well
Anthony

1. http://www.youtube.com/watch?v=Nzx0HAd3FiI

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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