Python numpy loadtxt失败，并带有日期时间 [英] Python numpy loadtxt fails with date time

问题描述

我正在尝试使用numpy loadtxt将csv文件加载到数组中。但是看来我无法正确加载日期时间。

I am trying to use numpy loadtxt to load a csv file into an array. But it seem i can't get the date time correctly loaded.

下面的示例演示了发生了什么。我做错了吗？

Below demonstrates what is happening. Did I do something wrong?

>>> s = StringIO("05/21/2007,03:27")
>>> np.loadtxt(s, delimiter=",", dtype={'names':('date','time'), 'formats':('datetime64[D]', 'datetime64[m]')})
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/numpy/lib/npyio.py", line 796, in loadtxt
items = [conv(val) for (conv, val) in zip(converters, vals)]
File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/numpy/lib/npyio.py", line 573, in <lambda>
  return lambda x: int(float(x))
ValueError: invalid literal for float(): 05/21/2007

推荐答案

还需要添加转换器，例如：

You need to also add converters, like:

from matplotlib.dates import strpdate2num
...
np.loadtxt(s, delimiter=",", converters={0:strpdate2num('%m/%d/%Y'), 1:...}, dtype= ...

当numpy看到您的dtype格式时of datetime [64]，它准备输出类型为numpy.datetime64的列。numpy.datetim64是numpy.integer的子类，并且loadtxt准备将该列作为整数处理，并带有以下内容：

When numpy sees your dtype format of datetime[64], it prepares to output a column of type numpy.datetime64. numpy.datetim64 is a subclass of numpy.integer, and loadtxt prepares to deal with that column as an integer with the following:

def _getconv(dtype):
    typ = dtype.type
    if issubclass(typ, np.bool_):
        return lambda x: bool(int(x))
    if issubclass(typ, np.uint64):
        return np.uint64
    if issubclass(typ, np.int64):
        return np.int64
    if issubclass(typ, np.integer):
        return lambda x: int(float(x))

    ...

何时到尝试在numpyio的第796行进行转换的点：

When it gets to the point of attempting conversion at line 796 in numpyio:

items = [conv(val) for (conv, val) in zip(converters, vals)]

它尝试使用 lambda x：int （float（x））处理输入。这样做时，它会尝试将您的日期（05/27/2007）转换为浮动日期，然后逐渐减少。上面的转换函数strpdate2num会将日期转换为数字表示形式。

it tries to uselambda x: int(float(x)) to handle the input. When it does that, it tries to cast your date (05/27/2007) to a float and peters out. The conversion function strpdate2num above will convert the date to a number representation.

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