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pythonstringarithmetic-expressions

Is it possible to place a string inside df[ ] in python?

I know this is a bad one. I really want to know if this is possible to do in python so I have two strings with arithmetic equation now I want to place them inside a df[ ]. df is a data frame Is this possible to do?

X = "'cars'+'bikes'*'planes'"

Now this should be placed like this below

X = df['cars']+df['bikes']*df['planes']

If possible how to do it?

Solution

  • I am assuming that you know the consequences of using eval.

    s =  "'cars'+'bikes'*'planes'"

df['out'] = eval(re.sub(r"([^+\-*\/]+)", r'df[\1]', s))

    What is does is basically substitutes df. It changes 'cars'+'bikes'*'planes' to df['cars']+df['bikes']*df['planes']. If you don't want to use eval you can parse the column names and operands like

    columns = re.findall(r"'([^+\-*\/]+)'", s)
operands = re.findall(r'([+\-*\/]+)', s)

    But in this case, you need to define operate precedence and create a tree to calculate the result.

    Update

    import re
import pandas as pd

s =  "'cars'+30*'bikes'-'planes'+20"
s2 = re.sub(r"('[^+\-*\/'\d]+')", r'df[\1]', s)

pd.eval(s2)