How to reverse boolean value in pandas.DataFrame

How can I reverse True/False value in pandas?

pandas.DataFrame is useful for handling table data.

With using it, we can handle CSV or Excel data as table data.

Sometimes table data has boolean data like True/False.

In order to reverse boolean values, what should we do ?

So today I will introduce about "How to reverse boolean value in pandas.DataFrame".

Author

Mid-carieer engineer (AI, system). Good at Python and SQL.

Prepare data

So how can we reverse boolean values in DataFrame ?

Before trying to reverse boolean values, prepare DataFrame that contains boolean column.

import pandas as pd

data_list1 = [
    ["a",True],
    ["b",True],
    ["c",False],
    ["d",True]
]
col_list1 = ["col1","col2"]
df1 = pd.DataFrame(data=data_list1, columns=col_list1)
print(df1)

#   col1   col2
# 0    a   True
# 1    b   True
# 2    c  False
# 3    d   True

Now we have sample data.

With using this data, we will try to reverse boolean values.

"not" operator can't reverse DataFrame boolean values

About "reverse", we will imagine not operator.

But not operator can't reverse DataFrame boolean values.

You can check like below.

df1["not_col2"] = not df1["col2"]

print(df1)

# ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

Like this, if we use not operator with pandas.DataFrame, it causes error.

According to the message, if we use .bool(), same error occurs.

print(df1["col2"].bool())

# ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

not operator is object-wise. So it couldn't do element-wise logical operation.

This must be a boolean scalar value, either True or False. It will raise a ValueError if the Series or DataFrame does not have exactly 1 element, or that element is not boolean (integer values 0 and 1 will also raise an exception).

Reference: pandas.DataFrame.bool — pandas 1.4.3 documentation

If it has 1 element like Series, we can reverse it by not.

df1_false = df1.loc[
  df1["col2"] ==  False
]
print(df1_false)
#   col1   col2
# 2    c  False

print(df1_false["col2"].bool())
# False

print(not df1_false["col2"].bool())
# True

But it doesn't mean that we could reverse boolean value in pandas.DataFrame.

How can we reverse it?

How to reverse boolean value in pandas.DataFrame

not operator can't reverse DataFrame boolean values.

So How can we reverse boolean value in pandas.DataFrame ?

The solution is ~.

With using ~, we can reverse boolean value in pandas.DataFrame.

df1["not_col2"] = ~df1["col2"]

print(df1)

#   col1   col2  not_col2
# 0    a   True     False
# 1    b   True     False
# 2    c  False      True
# 3    d   True     False

Like this sample code, we could reverse boolean values in col2 column.

Conclusion

Today I explained about "How to reverse boolean value in pandas.DataFrame".

Important points are below.

Once we learn it, it is easy to use.

There are some other articles about pandas.Dataframe or NumPy.ndarray.

If you interested in them, please read them.