CODEWITHSUNDEEP
pythonpandasdataframeseaborn
Jonas
Jonas

Reputation: 1529

pandas returns DataError when seaborn plots a dataframe made from lists

When I tried plotting a pandas dataframe in seaborn I got an DataError. I fixed the problem by recreating the dataframe from a Dictionary instead of using lists and a for loop. However, I still don't understand why I got the error in the first case. The two data frames look identical to me. Can somebody explain what happens here?

# When I create two seemingly identical data frames.
x = [0, 1, 2]
y = [3, 5, 7]
line_df1 = pd.DataFrame(columns=['x','y'])
for i in range(3):
    line_df1.loc[i] = [x[i], y[i]]

line_dict = {'x': [0, 1, 2], 'y': [3, 5, 7]}
line_df2 = pd.DataFrame(line_dict)

# they look identical when printed
print(line_df1)
print(line_df2)

>>    x  y
>> 0  0  3
>> 1  1  5
>> 2  2  7

>>    x  y
>> 0  0  3
>> 1  1  5
>> 2  2  7


# This first one throws a DataError...
sns.lineplot('x', 'y', data=line_df1)

# ..but this one does not.
sns.lineplot('x', 'y', data=line_df2)

Upvotes: 2

Views: 213

Answers (1)

jezrael
jezrael

Reputation: 862611

Problem is first values are objects, verified by DataFrame.dtypes:

print(line_df1.dtypes)
x    object
y    object
dtype: object

print(line_df2.dtypes)
x    int64
y    int64
dtype: object

Solution for correct working first solution is set dtype of empty DataFrame:

line_df1 = pd.DataFrame(columns=['x','y'], dtype=int)

But if performance is important, better is second solution, because update empty DataFrame is last instance:

6) updating an empty frame (e.g. using loc one-row-at-a-time)

Upvotes: 2

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