why can't I add 2 columns in pandas

Question

I have 2 columns in excel. I get an error from simply dividing them with pandas. What am I doing wrong?

import pandas as pd
import numpy as np

df = pd.read_excel('day.xlsx', sheet_name = 'day1')
df=pd.DataFrame(df)
df=df.rename(columns={0: 'Time', 'null': 'Temp', 'null.1':'Pressure'})
df['ratio']=df['Temp']/df['Pressure']

I am trying to create a third column 'ratio' from dividing 'Temp' with 'Pressure'.

Error message:

TypeError: unsupported operand type(s) for /: 'float' and 'str'

Are you getting the divide by zero error? [refer](https://stackoverflow.com/questions/13646347/python-divide-by-zero-error) — samkart, Jul 02 '19 at 05:19
Ensure that the columns 'Temp' and 'Pressure' are in numerical data type while importing and also make sure that none of the values in 'Pressure' is 0 or null. — Bigya Pradhan, Jul 02 '19 at 05:20
my error message: TypeError: unsupported operand type(s) for /: 'float' and 'str' — PandasKoala, Jul 02 '19 at 05:24
yes I do have null values but am I would prefer not to remove them — PandasKoala, Jul 02 '19 at 05:25
Can cross check the types of Temp Column and Pressure column? — Asnim P Ansari, Jul 02 '19 at 05:36
try to do `df['ratio'] = df['Temp*].astype(float)/df['Pressure'].astype(float)` — PV8, Jul 02 '19 at 05:46

score 0 · Answer 1 · answered Jul 02 '19 at 06:10

The error message is explicit:

TypeError: unsupported operand type(s) for /: 'float' and 'str'

It means that in df['Temp']/df['Pressure'] some (or all) of the values of df['Pressure'] are strings. You must first convert them to float, normally with astype(float) if all values represent acceptable float values or with to_numeric(coerce=True) if you want to be super safe: any non convertible string will be changed to NaN:

df['ratio']=df['Temp']/pd.to_numeric(df['Pressure'], coerce=True)

If you still get errors unsupported operand type(s) for /: 'str' and 'float', you will have to do the same conversion on df['Temp'].

why can't I add 2 columns in pandas

1 Answers1