[ase-users] sorting by number of atoms

[Jens Jørgen Mortensen]

On 02/18/2018 12:03 PM, Kim Nicoli via ase-users wrote:
> Hello,
>
> I am new to this ASE and I am trying to become confident with both the 
> environment and database. Therefore, I have a simple question:
> Is there a simple and straightforward way to sort (and save/update 
>  after the sorting) a database of atoms over the *number of atoms* in 
> a decreasing order? This is to say that I would like the longest 
> molecules to be on the first row and so on.
> I went through the documentation and I guess this should be feasible 
> and not that complicated but I am not getting the right syntax to do it.

You can loop over rows in a sorted order like this: 
"db.select(sort='-natoms')".  Or on the command line:

     $ ase db x.db -s natoms-

If you want to write a new sorted database:

     from ase.db import connect
     db1 = connect('x.db')
     with connect('x-sorted.db') as db2:
         for row in db1.select(sort='natoms'):
             db2.write(row)

Jens Jørgen

> Thanks for any help!
> With my best regards,
>
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