98 lines
3.1 KiB
Python
98 lines
3.1 KiB
Python
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# This file is part of Patsy
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# Copyright (C) 2011-2013 Nathaniel Smith <njs@pobox.com>
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# See file LICENSE.txt for license information.
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# This module sets up the namespace of stuff that is available to formulas by
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# default. All formulas are interpreted in an environment that acts as if
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# from patsy.builtins import *
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# has been executed. (Of course, you can also execute this yourself if you
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# want to use these in your regular code for some reason.)
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__all__ = ["I", "Q"]
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from patsy.contrasts import ContrastMatrix, Treatment, Poly, Sum, Helmert, Diff
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__all__ += ["ContrastMatrix", "Treatment", "Poly", "Sum", "Helmert", "Diff"]
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from patsy.categorical import C
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__all__ += ["C"]
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from patsy.state import center, standardize, scale
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__all__ += ["center", "standardize", "scale"]
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from patsy.splines import bs
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__all__ += ["bs"]
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from patsy.mgcv_cubic_splines import cr, cc, te
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__all__ += ["cr", "cc", "te"]
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def I(x):
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"""The identity function. Simply returns its input unchanged.
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Since Patsy's formula parser ignores anything inside a function call
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syntax, this is useful to 'hide' arithmetic operations from it. For
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instance::
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y ~ x1 + x2
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has ``x1`` and ``x2`` as two separate predictors. But in::
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y ~ I(x1 + x2)
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we instead have a single predictor, defined to be the sum of ``x1`` and
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``x2``."""
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return x
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def test_I():
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assert I(1) == 1
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assert I(None) is None
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def Q(name):
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"""A way to 'quote' variable names, especially ones that do not otherwise
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meet Python's variable name rules.
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If ``x`` is a variable, ``Q("x")`` returns the value of ``x``. (Note that
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``Q`` takes the *string* ``"x"``, not the value of ``x`` itself.) This
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works even if instead of ``x``, we have a variable name that would not
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otherwise be legal in Python.
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For example, if you have a column of data named ``weight.in.kg``, then you
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can't write::
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y ~ weight.in.kg
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because Python will try to find a variable named ``weight``, that has an
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attribute named ``in``, that has an attribute named ``kg``. (And worse
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yet, ``in`` is a reserved word, which makes this example doubly broken.)
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Instead, write::
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y ~ Q("weight.in.kg")
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and all will be well. Note, though, that this requires embedding a Python
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string inside your formula, which may require some care with your quote
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marks. Some standard options include::
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my_fit_function("y ~ Q('weight.in.kg')", ...)
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my_fit_function('y ~ Q("weight.in.kg")', ...)
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my_fit_function("y ~ Q(\\"weight.in.kg\\")", ...)
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Note also that ``Q`` is an ordinary Python function, which means that you
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can use it in more complex expressions. For example, this is a legal
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formula::
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y ~ np.sqrt(Q("weight.in.kg"))
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"""
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from patsy.eval import EvalEnvironment
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env = EvalEnvironment.capture(1)
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try:
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return env.namespace[name]
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except KeyError:
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raise NameError("no data named %r found" % (name,))
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def test_Q():
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a = 1
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assert Q("a") == 1
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assert Q("Q") is Q
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import pytest
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pytest.raises(NameError, Q, "asdfsadfdsad")
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