Hi, I ran into problems while trying to use Symbols as columns for a
pandas.DataFrame *.
This is probably not relevant to SymPy development itself, but rather just
use.
This seems to be a problem with both frameworks treating callable() objects
specially:
>>> import pandas as pd
>>> from sympy.abc import x, y
>>> gg = pd.DataFrame([[1,2],[3,3],[4,5]], columns=[x,y])
>>> print(gg[[x]]) # works fine, but returns a DataFrame
x
0 1
1 3
2 4
>>> print(gg[x])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "...\pandas\core\frame.py", line 1941, in __getitem__
key = com._apply_if_callable(key, self)
File "...\pandas\core\common.py", line 441, in _apply_if_callable
return maybe_callable(obj, **kwargs)
File "...sympy\core\symbol.py", line 158, in __call__
return Function(self.name)(*args)
File "...\sympy\core\function.py", line 761, in __new__
obj = super(AppliedUndef, cls).__new__(cls, *args, **options)
File "...\sympy\core\function.py", line 431, in __new__
pr = max(cls._should_evalf(a) for a in result.args)
File "...\sympy\core\function.py", line 431, in <genexpr>
pr = max(cls._should_evalf(a) for a in result.args)
File "...\sympy\core\function.py", line 449, in _should_evalf
if arg.is_Float:
File "...\pandas\core\generic.py", line 3081, in __getattr__
return object.__getattribute__(self, name)
AttributeError: 'DataFrame' object has no attribute 'is_Float'
The way to get a pd.Series would be:
>>> gg[[x]].iloc[:,0] # super uncomfortable...
0 1
1 3
2 4
Name: x, dtype: int64
Is there any reasonable way this interaction could be worked around? It
seems like a problem on the Pandas end, or maybe even designed
functionality, since functions work the same way (but fail faster):
>>> fg = pd.DataFrame([[1,2],[3,3],[4,5]], columns=[f,g])
>>> fg[[f]]
<function f at 0x000000000F79BEB8>
0 1
1 3
2 4
>>> fg[f]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "...\pandas\core\frame.py", line 1941, in __getitem__
key = com._apply_if_callable(key, self)
File "...\pandas\core\common.py", line 441, in _apply_if_callable
return maybe_callable(obj, **kwargs)
TypeError: f() takes no arguments (1 given)
But is there any way I can check whether the inputs are Symbols and
"freeze" them so that they become uncallable? Maybe some other workaround?
Thanks in advance.
* Why am I doing this? Partially due to curiosity, and partially because my
users might end up doing the same. It turns out that using Symbols as
variable placeholders in a data science workflow might be useful.
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