pandas read_csv 列 dtype 设置为十进制但转换为字符串

2022-01-13 00:00:00 python pandas csv decimal type-conversion

问题描述

我正在使用 pandas (v0.18.1) 从名为test.csv"的文件中导入以下数据:

I am using pandas (v0.18.1) to import the following data from a file called 'test.csv':

a,b,c,d
1,1,1,1.0

我已将列 'c' 和 'd' 的 dtype 设置为 'decimal.Decimal' 但它们返回为类型 'str'.

I have set the dtype to 'decimal.Decimal' for columns 'c' and 'd' but instead they return as type 'str'.

import pandas as pd
import decimal as D

df = pd.read_csv('test.csv', dtype={'a': int, 'b': float, 'c': D.Decimal, 'd': D.Decimal})

for i, v in df.iterrows():
    print(type(v.a), type(v.b), type(v.c), type(v.d))

结果:

`<class 'int'> <class 'float'> <class 'str'> <class 'str'>`

我还尝试在导入后显式转换为十进制，但没有成功(转换为浮点有效但不是十进制).

I have also tried converting to decimal explicitly after import with no luck (converting to float works but not decimal).

df.c = df.c.astype(float)
df.d = df.d.astype(D.Decimal)
for i, v in df.iterrows():
    print(type(v.a), type(v.b), type(v.c), type(v.d))

结果:

`<class 'int'> <class 'float'> <class 'float'> <class 'str'>`

以下代码将str"转换为decimal.Decimal"，所以我不明白为什么 pandas 的行为方式不同.

The following code converts a 'str' to 'decimal.Decimal' so I don't understand why pandas doesn't behave the same way. 

x = D.Decimal('1.0')
print(type(x))

结果:

`<class 'decimal.Decimal'>`

解决方案

我觉得你需要转换器:

import pandas as pd
import io
import decimal as D

temp = u"""a,b,c,d
           1,1,1,1.0"""

# after testing replace io.StringIO(temp) to filename
df = pd.read_csv(io.StringIO(temp), 
                 dtype={'a': int, 'b': float}, 
                 converters={'c': D.Decimal, 'd': D.Decimal})

print (df)
       a    b  c    d
    0  1  1.0  1  1.0

for i, v in df.iterrows():
    print(type(v.a), type(v.b), type(v.c), type(v.d))

    <class 'int'> <class 'float'> <class 'decimal.Decimal'> <class 'decimal.Decimal'>

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