ytree.frontends.ytree.arbor.YTreeArbor.get_yt_selection¶

YTreeArbor.get_yt_selection(above=None, below=None, equal=None, about=None, conditionals=None, data_source=None)[source]¶

Get a selection of halos meeting given criteria.

This function can be used to create database-like queries to search for halos meeting various criteria. It will return a YTCutRegion that can be queried to get field values for all halos meeting the selection criteria. The YTCutRegion can then be passed to get_nodes_from_selection to get all the TreeNode objects that meet the criteria.

If multiple criteria are provided, selected halos must meet all criteria.

To specify a custom data container, use the ytds attribute associated with the arbor to access the merger tree data as a yt dataset. For example:

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> ds = a.ytds

Parameters:	above (optional, list of tuples with (field, value, <units>)) – Halos meeting a given criterion must have field values at or above the provided limiting value. Each entry in the list must contain the field name, limiting value, and (optionally) units. below (optional, list of tuples with (field, value, <units>)) – Halos meeting a given criterion must have field values at or below the provided limiting value. Each entry in the list must contain the field name, limiting value, and (optionally) units. equal (optional, list of tuples with (field, value, <units>)) – Halos meeting a given criterion must have field values equal to the provided value. Each entry in the list must contain the field name, value, and (optionally) units. about (optional, list of tuples with (field, value, tolerance, <units>)) – Halos meeting a given criterion must have field values within the tolerance of the provided value. Each entry in the list must contain the field name, value, tolerance, and (optionally) units. conditionals (optional, list of strings) – A list of conditionals for constructing a custom `YTCutRegion`. This can be used instead of above/below/equal/about to create more complex selection criteria. See the Cut Regions section in the yt documentation for more information. The conditionals keyword can only be used if none of the first for selection keywords are given. data_source (optional, `YTDataContainer`) – The source yt data container to be used to make the cut region. If none given, the `all_data` container (i.e., the full dataset) is used.
Returns:	cr – The cut region associated with the provided selection criteria.
Return type:	`YTCutRegion`

Examples

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> # select halos above 1e12 Msun at redshift > 0.5
>>> sel = a.get_yt_selection(
...     above=[("mass", 1e13, "Msun"),
...            ("redshift", 0.5)])
>>> print (sel["halos", "mass"])
>>> print (sel["halos", "virial_radius"])

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> # select halos below 1e13 Msun at redshift > 1
>>> sel = a.get_yt_selection(
...     below=[("mass", 1e13, "Msun")],
...     above=[("redshift", 1)])
>>> print (sel["halos", "mass"])
>>> print (sel["halos", "virial_radius"])

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> # select phantom halos (a consistent-trees field)
>>> sel = a.get_yt_selection(equal=[("phantom", 1)])

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> # select halos with vmax of 200 +-10 km/s (i.e., 5%)
>>> sel = a.get_yt_selection(about=[("vmax", 200, "km/s", 0.05)])

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> # use a yt conditional
>>> sel = a.get_yt_selection(
...     conditionals=['obj["halos", "mass"] > 1e12'])

>>> import ytree
>>> a = ytree.load("arbor/arbor.h5")
>>> # select halos only within a sphere
>>> ds = a.ytds
>>> sphere = ds.sphere(ds.domain_center, (10, Mpc))
>>> sel = a.get_yt_selection(
...     above=[("mass", 1e13)],
...     data_source=sphere)
>>> # get the TreeNodes for the selection
>>> for node in a.get_nodes_from_selection(sel):
...     print (node["mass"])