ytree.data_structures.arbor.Arbor.add_derived_field

Arbor.add_derived_field(name, function, units=None, dtype=None, description=None, vector_components=None, force_add=True)[source]

Add a field that is a function of other fields.

Parameters:

  • name (string) – Field name.

  • function (callable) – The function to be called to generate the field. This function should take two arguments, the arbor and the data structure containing the dependent fields. See below for an example.

  • units (optional, string) – The units in which the field will be returned.

  • dtype (optional, type) – The data type of the field array. If none, use the default type set by Arbor._default_dtype.

  • description (optional, string) – A short description of the field.

  • vector_components (optional, list of strings) – If given, the field is assumed to be a vector field with the x/y/z component fields provided here. Default: None.

  • force_add (optional, bool) – If True, add field even if it already exists and warn the user and raise an exception if dependencies do not exist. If False, silently do nothing in both instances. Default: True.

Examples

>>> import ytree
>>> a = ytree.load("tree_0_0_0.dat")
>>> def _redshift(field, data):
...     return 1. / data["scale"] - 1
...
>>> a.add_derived_field("redshift", _redshift)
>>> print (a["redshift"])