Selecting particles

List of selection functions

pNbody provides several fonction to select particles:

function name	description
selectc	select particles from a condition
selecti	select particles from their index
selectp	select particles from their id
sub	select particles from their index
reduc	select a fraction of particles

Examples

To run the examples of this section, you must first move to the ~/pNbody_examples directory. If the latter does not exists, you can first create it with:

pNbody-examples-copy

and move inside the created directory.

Open a file containing particles and display it

>>> from pNbody import Nbody
>>> import numpy as np
>>> nb = Nbody("disk.dat",ftype='gadget')
>>> nb.cmcenter()
>>> nb.display(size=(100,100))

Select particles with a positive x coordinate

>>> nb = nb.selectc(nb.x()>0)
>>> nb.display(size=(100,100))

Select the first half of the particles, from their indices

>>> indices = np.arange(nb.nbody/2,dtype=int)
>>> nb = nb.selecti(indices)
>>> nb.display(size=(100,100))

Select particles based on their IDs

>>> nb = nb.selectp(lst=[161,171,191,201,211,221,241,261,301])
>>> print(nb.num)

Select a fraction of particles, reduce the number of particles by a factor 8, keeping 1 particles very 8

>>> nb = Nbody("disk.dat",ftype='gadget')
>>> nb.cmcenter()
>>> nb.display(size=(100,100))
>>> nb = nb.reduc(8)
>>> nb.display(size=(100,100))

Select a subset of particles with indices from 8 to 16

>>> nb = nb.sub(8,16)