多维数组排序 - Python

Question

from numpy import *list = array([["A", 25, 2], ["B", 25, 3], ["C", 10, 1], ["D", 50, 25]])如何按第二个元素除以第三个元素的降序大小对该数组进行排序。所以在这种情况下，正确的安排是：[“A”, 25, 2], [“C”, 10, 1], [“B”, 25, 3], [“D”, 50, 25]

Answer 1

import numpy as np

# Let's use a as the variable name so we don't override the list keyword

a = np.array([["A", 25, 2], ["B", 25, 3], ["C", 10, 1], ["D", 50, 25]])

# Need to convert values to int, because they are being casted as string

# in the original array (arrays only support one data type)

key_values = a[:,1].astype(int) / a[:,2].astype(int)

# Use argsort to get a sort index, then reverse the order to make it descending

index_array = np.argsort(key_values)[::-1]  # -1 reverses the order

print(a[index_array])

输出：

[['A' '25' '2']

 ['C' '10' '1']

 ['B' '25' '3']

 ['D' '50' '25']]

Answer 2

你能用熊猫吗？如果是这样，

import numpy as np

import pandas as pd

df = pd.DataFrame(np.array([["A", 25, 2], ["B", 25, 3], ["C", 10, 1], ["D", 50, 25]]))

df[1] = pd.to_numeric(df[1])

df[2] = pd.to_numeric(df[2])

df[3] = df[1] / df[2]

sorted_list = df.sort_values(by=3, ascending=False).values[:,:3]

print(sorted_list)

array([['A', 25, 2],

       ['C', 10, 1],

       ['B', 25, 3],

       ['D', 50, 25]], dtype=object)

请注意，这里我假设（基于我对问题的理解）您想要根据第二列除以第三列的值进行排序。如果是这种情况，输出示例的前两个元素将被翻转（因为 25/2 > 10/1）。