How to make a list out of the attribute of objects from a DataFrame column?-CodePudding

Yesterday I was wondering how to access to dictionary keys in a DataFrame column (link). The solution was to use .str[<key>] on the pandas Series and call the tolist() method afterwards. However this does not work with object attributes.

My goal is to get as an output a list of a specific attributes for each object in a panda Series.

Here is a sample code with the solution I am working with. I cast the whole object Series as a list and then iterate over it to get the specific attribute. Is there a way to access directly the attribute ?

class User:
    def __init__(self, name):
        self.name = name


df = pd.DataFrame({
    'col1': [User("Juan"), User("Karen"), User("Vince")]
})


myObjects = df['col1'].tolist()
myNames = [u.name for u in myObjects]

# Desired output
['Juan', 'Karen', 'Vince']

And when I try the dictionary solution :

myNames = df["col1"].str['name'].tolist()

# Output
[nan, nan, nan]

CodePudding user response：

You can use the attrgetter from operator library in combination with pandas.Series.map. This will map your inputs using the attrgetter, which returns a function that when called on the entries of col1 retrieve object attributes named name. Equivalent to lambda x: x.name

from operator import attrgetter
myNames = df["col1"].map(attrgetter("name")).tolist()

Output:

['Juan', 'Karen', 'Vince']

CodePudding user response：

I would not recommend your method as it only works if you change the class. Alternatively, you can use apply() for this:

myNames = list(df['col1'].apply(lambda x: x.name))

List:

['Juan', 'Karen', 'Vince']

The str method works only dictionaries, but not on objects. If you make your object convertible to a dictionary it would work. For example like this:

class User:
    def __init__(self, name):
        self.name = name
        
    def __iter__(self):
        yield 'name', self.name


df = pd.DataFrame({
    'col1': [User("Juan"), User("Karen"), User("Vince")]
})

result = list(df['col1'].map(dict).str['name'])

CodePudding user response：

You can also try:

df['col1'].map(lambda x: x.name).to_list()