pandas 理解熊猫数据帧中的数学错误
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understanding math errors in pandas dataframes
提问by user3654387
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...
我正在尝试从其他列的 Pandas 数据框中生成一个新列，但出现了一些我不明白的数学错误。这是问题的快照和一些简化的诊断...
I can generate a data frame that looks pretty good:
我可以生成一个看起来不错的数据框：
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
I can do simple math (i.e. degrees to radians):
我可以做简单的数学运算（即度数到弧度）：
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
But I can't convert from degrees to radians using the python math library:
但我无法使用 python 数学库从度数转换为弧度：
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'>
And can't even convert the values to floats to try to force it to work:
甚至不能将值转换为浮点数以试图强制它工作：
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'>
I'm sure there must be a simple explanation and would appreciate your help in finding it. Thanks!
我相信必须有一个简单的解释，并希望您能帮助找到它。谢谢！
回答by unutbu
math functions such as math.radiansexpect a numeric value such as a float, not a sequence such as a pandas.Series.
诸如math.radians 之类的数学函数需要一个数字值，例如一个浮点数，而不是一个诸如 a 之类的序列pandas.Series。
Instead, you could use numpy.radians, since numpy.radianscan accept an array as input:
相反，您可以使用numpy.radians，因为numpy.radians可以接受数组作为输入：
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
Only Series of length 1 can be converted to a float. So while
this works,
只有长度为 1 的系列才能转换为float. 所以虽然这有效，
In [103]: math.radians(pd.Series([1]))
Out[103]: 0.017453292519943295
in general it does not:
一般来说，它不会：
In [104]: math.radians(pd.Series([1,2]))
TypeError: cannot convert the series to <type 'float'>
math.radiansis calling floaton its argument. Note that you get the same error calling floaton pd.Series([1,2]):
math.radians正在呼吁float其论点。请注意，您在调用float时会遇到相同的错误pd.Series([1,2])：
In [105]: float(pd.Series([1,2]))
TypeError: cannot convert the series to <type 'float'>
回答by AnthonySCaldera
I had a similar issue but was using a custom function. The solution was to use the applyfunction:
我有一个类似的问题，但使用的是自定义函数。解决方案是使用该apply功能：
def monthdiff(x):
z = (int(x/100) * 12) + (x - int(x/100) * 100)
return z
series['age'].apply(monthdiff)
Now, I have a new column with my simple (yet beautiful) calculation applied to every line in the data frame!
现在，我有一个新列，我的简单（但漂亮）的计算应用于数据框中的每一行！
回答by ANNE ANGELINA
try:
尝试：
pd.to_numeric()
When I got the same error, this is what worked for me.
当我遇到同样的错误时，这对我有用。
