数据帧将列类型转换为字符串或类别

Question

如何将数据帧的单个列转换为字符串类型？在下面住房数据的df中，我需要将zipcode转换为字符串，以便在运行线性回归时，zipcode被视为分类的，而不是数字的。谢谢

df = pd.DataFrame({'zipcode': {17384: 98125, 2680: 98107, 722: 98005, 18754: 98109, 14554: 98155}, 'bathrooms': {17384: 1.5, 2680: 0.75, 722: 3.25, 18754: 1.0, 14554: 2.5}, 'sqft_lot': {17384: 1650, 2680: 3700, 722: 51836, 18754: 2640, 14554: 9603}, 'bedrooms': {17384: 2, 2680: 2, 722: 4, 18754: 2, 14554: 4}, 'sqft_living': {17384: 1430, 2680: 1440, 722: 4670, 18754: 1130, 14554: 3180}, 'floors': {17384: 3.0, 2680: 1.0, 722: 2.0, 18754: 1.0, 14554: 2.0}})
print (df)
       bathrooms  bedrooms  floors  sqft_living  sqft_lot  zipcode
722         3.25         4     2.0         4670     51836    98005
2680        0.75         2     1.0         1440      3700    98107
14554       2.50         4     2.0         3180      9603    98155
17384       1.50         2     3.0         1430      1650    98125
18754       1.00         2     1.0         1130      2640    98109

Answer 1

与熊猫一起>；=1.0现在有一个专用的字符串数据类型：

1）您可以使用.astype('string')将列转换为该字符串数据类型：

df['zipcode'] = df['zipcode'].astype('string')

2）这与使用str设置对象数据类型不同：

df['zipcode'] = df['zipcode'].astype(str)

3）要更改为分类数据类型请使用：

df['zipcode'] = df['zipcode'].astype('category')

当您查看数据帧的信息时，可以看到数据类型的这种差异：

df = pd.DataFrame({
    'zipcode_str': [90210, 90211] ,
    'zipcode_string': [90210, 90211],
    'zipcode_category': [90210, 90211],
})

df['zipcode_str'] = df['zipcode_str'].astype(str)
df['zipcode_string'] = df['zipcode_str'].astype('string')
df['zipcode_category'] = df['zipcode_category'].astype('category')

df.info()

# you can see that the first column has dtype object
# while the second column has the new dtype string
# the third column has dtype category
 #   Column            Non-Null Count  Dtype   
---  ------            --------------  -----   
 0   zipcode_str       2 non-null      object  
 1   zipcode_string    2 non-null      string  
 2   zipcode_category  2 non-null      category
dtypes: category(1), object(1), string(1)

从文档中：

The 'string' extension type solves several issues with object-dtype NumPy arrays:

1. You can accidentally store a mixture of strings and non-strings in an object dtype array. A StringArray can only store strings.

2. object dtype breaks dtype-specific operations like DataFrame.select_dtypes(). There isn’t a clear way to select just text while excluding non-text, but still object-dtype columns.

3. When reading code, the contents of an object dtype array is less clear than string.
   

有关使用新字符串数据类型的更多信息，请参见： https://pandas.pydata.org/pandas-docs/stable/user_guide/text.html

Answer 2

您需要^{}：

df['zipcode'] = df.zipcode.astype(str)
#df.zipcode = df.zipcode.astype(str)

---

要转换为categorical，请执行以下操作：

df['zipcode'] = df.zipcode.astype('category')
#df.zipcode = df.zipcode.astype('category')

另一个解决方案是^{}：

df['zipcode'] = pd.Categorical(df.zipcode)

数据样本：

import pandas as pd

df = pd.DataFrame({'zipcode': {17384: 98125, 2680: 98107, 722: 98005, 18754: 98109, 14554: 98155}, 'bathrooms': {17384: 1.5, 2680: 0.75, 722: 3.25, 18754: 1.0, 14554: 2.5}, 'sqft_lot': {17384: 1650, 2680: 3700, 722: 51836, 18754: 2640, 14554: 9603}, 'bedrooms': {17384: 2, 2680: 2, 722: 4, 18754: 2, 14554: 4}, 'sqft_living': {17384: 1430, 2680: 1440, 722: 4670, 18754: 1130, 14554: 3180}, 'floors': {17384: 3.0, 2680: 1.0, 722: 2.0, 18754: 1.0, 14554: 2.0}})

print (df)
       bathrooms  bedrooms  floors  sqft_living  sqft_lot  zipcode
722         3.25         4     2.0         4670     51836    98005
2680        0.75         2     1.0         1440      3700    98107
14554       2.50         4     2.0         3180      9603    98155
17384       1.50         2     3.0         1430      1650    98125
18754       1.00         2     1.0         1130      2640    98109

print (df.dtypes)
bathrooms      float64
bedrooms         int64
floors         float64
sqft_living      int64
sqft_lot         int64
zipcode          int64
dtype: object

df['zipcode'] = df.zipcode.astype('category')

print (df)
       bathrooms  bedrooms  floors  sqft_living  sqft_lot zipcode
722         3.25         4     2.0         4670     51836   98005
2680        0.75         2     1.0         1440      3700   98107
14554       2.50         4     2.0         3180      9603   98155
17384       1.50         2     3.0         1430      1650   98125
18754       1.00         2     1.0         1130      2640   98109

print (df.dtypes)
bathrooms       float64
bedrooms          int64
floors          float64
sqft_living       int64
sqft_lot          int64
zipcode        category
dtype: object

Answer 3

先前的回答侧重于名义数据（例如无序数据）。如果有理由对顺序变量施加顺序，则可以使用：

# Transform to category
df['zipcode_category'] = df['zipcode_category'].astype('category')

# Add ordered category
df['zipcode_ordered'] = df['zipcode_category']

# Setup the ordering
df.zipcode_ordered.cat.set_categories(
    new_categories = [90211, 90210], ordered = True, inplace = True
)

# Output IDs
df['zipcode_ordered_id'] = df.zipcode_ordered.cat.codes
print(df)
#  zipcode_category zipcode_ordered  zipcode_ordered_id
#            90210           90210                   1
#            90211           90211                   0

有关设置有序类别的更多详细信息，请访问pandas网站：

https://pandas.pydata.org/pandas-docs/stable/user_guide/categorical.html#sorting-and-order