Seaborn 热图引发意外错误

我正在尝试执行以下代码：

import seaborn as sns
import pandas as pd
import numpy as np
year = range(1949,1961)
month = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
passengers = pd.Series(np.random.randint(100, 1000, len(year)*len(month)), name='passengers')
years = pd.Series(year * len(month), name='years')
months = pd.Series(month * len(year), name='months').sort_values().reset_index(drop=True)
df = pd.DataFrame([years, months, passengers]).T
df_flight = df.pivot(index="months", columns="years", values="passengers")
sns.heatmap(df_flight, annot=True, fmt="d", linewidths=.5)

它引发了意外错误：

TypeError: ufunc 'isnan' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

请解释我的代码中有什么错误。

您需要将值转换为int by astype http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.astype.html， 因为strings:

sns.heatmap(df_flight.astype(int), annot=True, fmt="d", linewidths=.5)

问题是如果使用DataFrame以这种方式构造函数，并且值至少有一列是strings，然后将所有值转换为strings too:

df = pd.DataFrame([years, months, passengers]).T

print (df.dtypes)
years         object
months        object
passengers    object

解决方案是使用concat http://pandas.pydata.org/pandas-docs/stable/generated/pandas.concat.html or DataFrame构造函数与dicts:

df = pd.concat([years, months, passengers], axis=1)

print (df.dtypes)
years          int64
months        object
passengers     int32
dtype: object

...

sns.heatmap(df_flight, annot=True, fmt="d", linewidths=.5)

Or:

df = pd.DataFrame({'years':years, 'months':months, 'passengers':passengers})

print (df.dtypes)
months        object
passengers     int32
years          int64
dtype: object

...

sns.heatmap(df_flight, annot=True, fmt="d", linewidths=.5)