ufunc 'divide' 不支持输入类型......尝试获取 NumPy 平均值时出现错误问题

Question

I am new to Numpy and I have been trying to get the average of an array I derived from another array.

This is the code that have been giving me error: "ufunc 'divide' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe'' "

import numpy as np
import pandas as pd
​
cars = pd.read_csv('data/co2_emissions_canada.csv')
cars_makes = cars['Make'].to_numpy()
cars_models = cars['Model'].to_numpy()
cars_classes = cars['Vehicle Class'].to_numpy()
cars_engine_sizes = cars['Engine Size(L)'].to_numpy()
cars_cylinders = cars['Cylinders'].to_numpy()
cars_transmissions = cars['Transmission'].to_numpy()
cars_fuel_types = cars['Fuel Type'].to_numpy()
cars_fuel_consumption = cars['Fuel Consumption Comb (L/100 km)'].to_numpy()
cars_co2_emissions = cars['CO2 Emissions(g/km)'].to_numpy()
​
#the median of the cars_engine_sizes
print(np.median(cars_engine_sizes))

#the average fuel consumption for regular gasoline (Fuel Type = X), #premium gasoline (Z), ethanol (E), and diesel (D)? 

fuel_typesx=np.array(cars_fuel_types[cars_fuel_types=='X'])
print(np.average(fuel_typesx))

fuel_typesz=np.array(cars_fuel_types[cars_fuel_types=='Z'])
print(np.average(fuel_typesz))

fuel_typese=np.array(cars_fuel_types[cars_fuel_types=='E'])
print(np.average(fuel_typese))

please, what am i missing

Answer 1

I'm guessing the FULL error message looks something like this:

In [753]: np.average(np.array(['A','B','C','A'],dtype=object))
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [753], in <cell line: 1>()
----> 1 np.average(np.array(['A','B','C','A'],dtype=object))

File <__array_function__ internals>:5, in average(*args, **kwargs)

File ~\anaconda3\lib\site-packages\numpy\lib\function_base.py:380, in average(a, axis, weights, returned)
    377 a = np.asanyarray(a)
    379 if weights is None:
--> 380     avg = a.mean(axis)
    381     scl = avg.dtype.type(a.size/avg.size)
    382 else:

File ~\anaconda3\lib\site-packages\numpy\core\_methods.py:191, in _mean(a, axis, dtype, out, keepdims, where)
    189         ret = ret.dtype.type(ret / rcount)
    190 else:
--> 191     ret = ret / rcount
    193 return ret

TypeError: ufunc 'true_divide' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

cars_fuel_types comes from a dataframe, and evidently contains strings like 'E'. So it is object dtype. Even if you select like values, you can't take an 'average'.

average takes the sum of values and divides by the count. sum for python strings is concatenation, not some sort of math.

In [754]: np.sum(np.array(['A','B','C','A'],dtype=object))
Out[754]: 'ABCA'