📅 最后修改于: 2020-10-27 04:13:05 🧑 作者: Mango
Numpy提供了多种用于排序和搜索的功能。有多种排序算法，例如quicksort，merge sort和heapsort，它们是使用numpy.sort()函数的。
必须在函数调用中提及排序操作中使用的排序算法的种类。
让我们讨论在numpy.sort()中实现的排序算法
| SN | Algorithm | Worst case complexity |
|---|---|---|
| 1 | Quick Sort | O (n ^ 2) |
| 2 | Merge Sort | O (n * log(n)) |
| 3 | Heap Sort | O (n * log(n)) |
下面给出了使用numpy.sort()函数的语法。
numpy.sort(a, axis, kind, order)
它接受以下参数。
| SN | Parameter | Description |
|---|---|---|
| 1 | input | It represents the input array which is to be sorted. |
| 2 | axis | It represents the axis along which the array is to be sorted. If the axis is not mentioned, then the sorting is done along the last available axis. |
| 3 | kind | It represents the type of sorting algorithm which is to be used while sorting. The default is quick sort. |
| 4 | order | It represents the filed according to which the array is to be sorted in the case if the array contains the fields. |
考虑以下示例。
import numpy as np
a = np.array([[10,2,3],[4,5,6],[7,8,9]])
print("Sorting along the columns:")
print(np.sort(a))
print("Sorting along the rows:")
print(np.sort(a, 0))
data_type = np.dtype([('name', 'S10'),('marks',int)])
arr = np.array([('Mukesh',200),('John',251)],dtype = data_type)
print("Sorting data ordered by name")
print(np.sort(arr,order = 'name'))
输出：
Sorting along the columns:
[[ 2 3 10]
[ 4 5 6]
[ 7 8 9]]
Sorting along the rows:
[[ 4 2 3]
[ 7 5 6]
[10 8 9]]
Sorting data ordered by name
[(b'John', 251) (b'Mukesh', 200)]
此函数用于对输入数组执行间接排序，即，它返回数据索引数组，该索引用于构造排序后的数据数组。
考虑以下示例。
import numpy as np
a = np.array([90, 29, 89, 12])
print("Original array:\n",a)
sort_ind = np.argsort(a)
print("Printing indices of sorted data\n",sort_ind)
sort_a = a[sort_ind]
print("printing sorted array")
for i in sort_ind:
print(a[i],end = " ")
输出：
Original array:
[90 29 89 12]
Printing indices of sorted data
[3 1 2 0]
printing sorted array
12 29 89 90
此函数用于间接使用键序列对数组进行排序。该函数的执行类似于numpy.argsort()，该函数返回已排序数据的索引数组。
考虑以下示例。
import numpy as np
a = np.array(['a','b','c','d','e'])
b = np.array([12, 90, 380, 12, 211])
ind = np.lexsort((a,b))
print("printing indices of sorted data")
print(ind)
print("using the indices to sort the array")
for i in ind:
print(a[i],b[i])
输出：
printing indices of sorted data
[0 3 1 4 2]
using the indices to sort the array
a 12
d 12
b 90
e 211
c 380
此函数用于从数组中查找非零元素的位置。
考虑以下示例。
import numpy as np
b = np.array([12, 90, 380, 12, 211])
print("printing original array",b)
print("printing location of the non-zero elements")
print(b.nonzero())
输出：
printing original array [ 12 90 380 12 211]
printing location of the non-zero elements
(array([0, 1, 2, 3, 4]),)
此函数用于返回满足特定条件的所有元素的索引。
考虑以下示例。
import numpy as np
b = np.array([12, 90, 380, 12, 211])
print(np.where(b>12))
c = np.array([[20, 24],[21, 23]])
print(np.where(c>20))
输出：
(array([1, 2, 4]),)
(array([0, 1, 1]), array([1, 0, 1]))