防止pandas在read_csv中自动推断类型

Question

我有一个#-separated文件有三列:第一个是整数,第二个看起来像浮点数,但不是,第三个是字符串.我尝试将其直接加载到python中pandas.read_csv

In [149]: d = pandas.read_csv('resources/names/fos_names.csv',  sep='#', header=None, names=['int_field', 'floatlike_field', 'str_field'])

In [150]: d
Out[150]: 
<class 'pandas.core.frame.DataFrame'>
Int64Index: 1673 entries, 0 to 1672
Data columns:
int_field          1673  non-null values
floatlike_field    1673  non-null values
str_field          1673  non-null values
dtypes: float64(1), int64(1), object(1)

pandas尝试智能并自动将字段转换为有用的类型.问题是我实际上并不希望它这样做(如果我这样做,我会使用这个converters论点).如何防止pandas自动转换类型？

Answer 1

我计划在pandas 0.10即将进行的文件解析器引擎大修中添加显式列dtypes.无法100%承诺,但新基础设施的整合应该非常简单(http://wesmckinney.com/blog/?p=543).

Answer 2

我认为你最好的选择是首先使用numpy将数据作为记录数组读取.

# what you described:
In [15]: import numpy as np
In [16]: import pandas
In [17]: x = pandas.read_csv('weird.csv')

In [19]: x.dtypes
Out[19]: 
int_field            int64
floatlike_field    float64  # what you don't want?
str_field           object

In [20]: datatypes = [('int_field','i4'),('floatlike','S10'),('strfield','S10')]

In [21]: y_np = np.loadtxt('weird.csv', dtype=datatypes, delimiter=',', skiprows=1)

In [22]: y_np
Out[22]: 
array([(1, '2.31', 'one'), (2, '3.12', 'two'), (3, '1.32', 'three ')], 
      dtype=[('int_field', '<i4'), ('floatlike', '|S10'), ('strfield', '|S10')])

In [23]: y_pandas = pandas.DataFrame.from_records(y_np)

In [25]: y_pandas.dtypes
Out[25]: 
int_field     int64
floatlike    object  # better?
strfield     object