python - 使用 iloc 更改特定列的数据类型

Question

我想通过 iloc 更改我的 DataFrame 中某些列的数据类型。但是当我尝试这个时，dtype 没有改变(它仍然是对象):

import pandas as pd
names = ['sepal-length', 'sepal-width', 'petal-length', 'petal-width', 'class']
df = pd.read_csv('iris.csv', names=names, header=None)
df = df[1:]

In [11]: df.head()
Out[11]:
   sepal-length  sepal-width  petal-length  petal-width   class
1           5.1          3.5           1.4          0.2  setosa
2           4.9          3.0           1.4          0.2  setosa
3           4.7          3.2           1.3          0.2  setosa
4           4.6          3.1           1.5          0.2  setosa
5           5.0          3.6           1.4          0.2  setosa


In [12]: df.iloc[:,:-1] = df.iloc[:,:-1].astype(float)
# No Error

In [13]: df.dtypes  # still object dtype
Out[13]:
sepal-length    object
sepal-width     object
petal-length    object
petal-width     object
class           object
dtype: object

注意:不用iloc我也能做到，但是太长了:

df[['sepal-length', 'sepal-width', 'petal-length', 'petal-width']] = df[['sepal-length', 'sepal-width', 'petal-length', 'petal-width']].astype(float)

Answer 1

您可以使用 infer_objects :

In [11]: df.infer_objects()
Out[11]:
   sepal-length  sepal-width  petal-length  petal-width   class
1           5.1          3.5           1.4          0.2  setosa
2           4.9          3.0           1.4          0.2  setosa
3           4.7          3.2           1.3          0.2  setosa
4           4.6          3.1           1.5          0.2  setosa
5           5.0          3.6           1.4          0.2  setosa

In [12]: df.infer_objects().dtypes
Out[12]:
sepal-length    float64
sepal-width     float64
petal-length    float64
petal-width     float64
class            object
dtype: object

---

问题是虽然右侧是正确的:

In [21]: df.iloc[:,:-1].astype(float).dtypes
Out[21]:
sepal-length    float64
sepal-width     float64
petal-length    float64
petal-width     float64
dtype: object

分配 df.iloc[:,:-1] = 正在更新现有列并且不更改它们的 dtype。