了解pandas数据帧中的数学错误 [英] understanding math errors in pandas dataframes
问题描述
我正在尝试在其他列的pandas数据框中生成一个新列，并且我得到一些我不理解的数学错误。这是问题的快照和一些简化的诊断......
I'm trying to generate a new column in a pandas dataframe from other columns and am getting some math errors that I don't understand. Here is a snapshot of the problem and some simplifying diagnostics...
我可以生成一个看起来相当不错的数据框：
I can generate a data frame that looks pretty good:
import pandas
import math as m
data = {'loc':['1','2','3','4','5'],
'lat':[61.3850,32.7990,34.9513,14.2417,33.7712],
'lng':[-152.2683,-86.8073,-92.3809,-170.7197,-111.3877]}
frame = pandas.DataFrame(data)
frame
Out[15]:
lat lng loc
0 61.3850 -152.2683 1
1 32.7990 -86.8073 2
2 34.9513 -92.3809 3
3 14.2417 -170.7197 4
4 33.7712 -111.3877 5
5 rows × 3 columns
我可以做简单的数学运算（即度数到弧度）：
I can do simple math (i.e. degrees to radians):
In [32]:
m.pi*frame.lat/180.
Out[32]:
0 1.071370
1 0.572451
2 0.610015
3 0.248565
4 0.589419
Name: lat, dtype: float64
但我无法使用python数学库将度数转换为弧度：
But I can't convert from degrees to radians using the python math library:
In [33]:
m.radians(frame.lat)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-33-99a986252f80> in <module>()
----> 1 m.radians(frame.lat)
/Users/user/anaconda/lib/python2.7/site-packages/pandas/core/series.pyc in wrapper(self)
72 return converter(self.iloc[0])
73 raise TypeError(
---> 74 "cannot convert the series to {0}".format(str(converter)))
75 return wrapper
76
TypeError: cannot convert the series to <type 'float'>
甚至无法将值转换为浮点数以试图强制它起作用：
And can't even convert the values to floats to try to force it to work:
In [34]:
float(frame.lat)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-34-3311aee92f31> in <module>()
----> 1 float(frame.lat)
/Users/user/anaconda/lib/python2.7/site-packages/pandas/core/series.pyc in wrapper(self)
72 return converter(self.iloc[0])
73 raise TypeError(
---> 74 "cannot convert the series to {0}".format(str(converter)))
75 return wrapper
76
TypeError: cannot convert the series to <type 'float'>
我确信必须有一个简单的解释，并感谢您的帮助。谢谢！
I'm sure there must be a simple explanation and would appreciate your help in finding it. Thanks!
推荐答案
数学函数，例如 math.radians 期望一个数值，例如float，而不是像 pandas.Series 。
math functions such as math.radians expect a numeric value such as a float, not a sequence such as a pandas.Series.
相反，您可以使用 numpy.radians ，因为 numpy.radians 可以接受数组作为输入：
Instead, you could use numpy.radians, since numpy.radians can accept an array as input:
In [95]: np.radians(frame['lat'])
Out[95]:
0 1.071370
1 0.572451
2 0.610015
3 0.248565
4 0.589419
Name: lat, dtype: float64
只有长度为1的系列可以转换为 float 。因此，虽然这是有效的
，
Only Series of length 1 can be converted to a float. So while
this works,
In [103]: math.radians(pd.Series([1]))
Out[103]: 0.017453292519943295
一般不会：
In [104]: math.radians(pd.Series([1,2]))
TypeError: cannot convert the series to <type 'float'>
math.radians 在其参数上调用 float 。请注意，在 pd.Series（[1,2]）上调用 float 时会出现相同的错误：
math.radians is calling float on its argument. Note that you get the same error calling float on pd.Series([1,2]):
In [105]: float(pd.Series([1,2]))
TypeError: cannot convert the series to <type 'float'>
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