Calling round(), ceiling(), floor(), min(), max() in pandas eval

问题

As title says, Is there a way to support round, ceiling, min, max, floor functions in pandas eval.

DataFrame:

import pandas as pd
import numexpr as ne
op_d = {'ID': [1, 2,3],'V':['F','G','H'],'AAA':[0,1,1],'E':[102014,112019,122017] ,'D':['2019/02/04','2019/02/01','2019/01/01'],'DD':['2019-12-01','2016-05-31','2015-02-15'],'CurrentRate':[7.5,2,2],'NoteRate':[2,3,3],'BBB':[0,00,4],'Q1':[2,8,00],'Q2':[3,5,7],'Q3':[5,6,8]}
df = pd.DataFrame(data=op_d)

abs() and sqrt() function works with pandas eval. i.e.

df.eval('TT = abs(sqrt(Q1+Q2)-Q2)',inplace=True)
df

can anyone suggest how to access rest of the functions in eval? I also tried 'local_dict' in eval to see if I can define custom functions and call them but it didn't work.

Note:

Arithmetic operations inside these functions are necessary (i.e. sum, multiplication, div of two columns).
I am aware of issues around usage of 'eval' functions and taking necessary measurements.

回答1:

You can't

DataFrame.eval only supports a limited set of math operations

Arithmetic operations except for the left shift (<<) and right shift (>>) operators, e.g., df + 2 * pi / s ** 4 % 42 - the_golden_ratio

Math functions: sin, cos, exp, log, expm1, log1p, sqrt, sinh, cosh, tanh, arcsin, arccos, arctan, arccosh, arcsinh, arctanh, abs, arctan2 and log10.

If it's not on that list you can't call it beacause "Function calls other than math functions [are not allowed syntax]"

That being said, it might be possible to implement some of those functions in terms of more basic operations. Here I've implemented an eval equivalent of np.sign. But IMO that obfuscates the operation far too much and isn't very useful, so really you need to move away from eval

回答2:

With the help of 'py_expression_eval' libary, I was able to work out arithmatic operations inside user defined functions.

from py_expression_eval import Parser
parser = Parser()

dct = {'Q1':df['Q1'],'Q2':df['Q2'],'max':max1,'round':getround}
df['check']=parser.parse('round(Q1/Q2)').evaluate(dct)

library source: https://github.com/Axiacore/py-expression-eval

Hope this helps others.

来源：https://stackoverflow.com/questions/60762008/calling-round-ceiling-floor-min-max-in-pandas-eval

标签

python

pandas

eval