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pythonpandas
Parseltongue
Parseltongue

Reputation: 11657

Python Pandas: Resolving "List Object has no Attribute 'Loc'"

I import a CSV as a DataFrame using:

import numpy as np
import pandas as pd

df = pd.read_csv("test.csv")

Then I'm trying to do a simple replace based on IDs:
df.loc[df.ID == 103, ['fname', 'lname']] = 'Michael', 'Johnson'

I get the following error:

AttributeError: 'list' object has no attribute 'loc'

Note, when I do print pd.version() I get 0.12.0, so it's not a problem (at least as far as I understand) with having pre-11 version. Any ideas?

Upvotes: 5

Views: 62933

Answers (3)

Carst
Carst

Reputation: 1604

To pickup from the comment: "I was doing this:"

df = [df.hc== 2]

What you create there is a "mask": an array with booleans that says which part of the index fulfilled your condition.

To filter your dataframe on your condition you want to do this:

df = df[df.hc == 2]

A bit more explicit is this:

mask = df.hc == 2
df = df[mask]

If you want to keep the entire dataframe and only want to replace specific values, there are methods such replace: Python pandas equivalent for replace. Also another (performance wise great) method would be creating a separate DataFrame with the from/to values as column and using pd.merge to combine it into the existing DataFrame. And using your index to set values is also possible:

df[mask]['fname'] = 'Johnson'

But for a larger set of replaces you would want to use one of the two other methods or use "apply" with a lambda function (for value transformations). Last but not least: you can use .fillna('bla') to rapidly fill up NA values.

Upvotes: 5

Jeff
Jeff

Reputation: 128958

@Boud answer is correct. Loc assignment works fine if the right-hand-side list matches the number of replacing elements

In [56]: df = DataFrame(dict(A =[1,2,3], B = [4,5,6], C = [7,8,9]))

In [57]: df
Out[57]: 
   A  B  C
0  1  4  7
1  2  5  8
2  3  6  9

In [58]: df.loc[1,['A','B']] = -1,-2

In [59]: df
Out[59]: 
   A  B  C
0  1  4  7
1 -1 -2  8
2  3  6  9

Upvotes: 1

Zeugma
Zeugma

Reputation: 32095

The traceback indicates to you that df is a list and not a DataFrame as expected in your line of code.

It means that between df = pd.read_csv("test.csv") and df.loc[df.ID == 103, ['fname', 'lname']] = 'Michael', 'Johnson' you have other lines of codes that assigns a list object to df. Review that piece of code to find your bug

Upvotes: 1

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