Python程式旋轉列表元素-Python教學-PHP中文網

Python程式旋轉列表元素

在Python中，可以使用清單來在單一變數中維護多個項目。清單是Python的四種內建資料類型之一，用於儲存資料集合。另外三種類型，元組、集合和字典，各自有不同的功能。列表使用方括號進行建構。由於清單不必是同質的，它們是Python中最有用的工具。一個列表可以包含字串、物件和整數等資料類型。列表可以在生成後進行修改，因為它們是可變的。

本文的重點是速記和用一句話或一個字來表達這個概念的許多捷徑。這個操作對程式設計師來說非常重要，可以完成許多工作。我們將使用Python來展示四種不同的方法來完成這個任務。

Using The List Comprehension

在使用這種方法時，我們只需要在特定位置旋轉後重新分配清單中每個元素的索引。由於其較小的實現，這種方法在完成任務中起著重要作用。

Algorithm

Defining a list first.
#Use the list comprehension.
#For applying two different sides right(i-index) and left(i index).
Print the output list.

文法

#左旋轉

list_1 = [list_1[(i + 3) % len(list_1)]

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#For right rotate

list_1 = [list_1[(i - 3) % len(list_1)]

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Example

Here, in this code we have used the list comprehension to rotate the elements in a list that is the right and left rotate. For loop is used to iterate through the list of elements.

list_1 = [10, 14, 26, 37, 42]
print (" Primary list : " + str(list_1))
list_1 = [list_1[(i + 3) % len(list_1)]
   for i, x in enumerate(list_1)]
print ("Output of the list after left rotate by 3 : " + str(list_1))
list_1 = [list_1[(i - 3) % len(list_1)]
   for i, x in enumerate(list_1)]
print ("Output of the list after right rotate by 3(back to primary list) : "+str(list_1))
list_1 = [list_1[(i + 2) % len(list_1)]
   for i, x in enumerate(list_1)]
print ("Output of the list after left rotate by 2 : " + str(list_1))
list_1 = [list_1[(i - 2) % len(list_1)]
   for i, x in enumerate(list_1)]
print ("Output of the list after right rotate by 2 : "+ str(list_1))

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輸出

Primary list : [10, 14, 26, 37, 42]
Output of the list after left rotate by 3 : [37, 42, 10, 14, 26]
Output of the list after right rotate by 3(back to primary list) : [10, 14, 26, 37, 42]
Output of the list after left rotate by 2 : [26, 37, 42, 10, 14]
Output of the list after right rotate by 2 : [10, 14, 26, 37, 42]

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Here, in this code we have used the list comprehension to rotate the elements in a list that is the right and left rotate. For loop is used to iterate through the list of elements.

使用切片

This specific technique is the standard technique. With the rotation number, it simply joins the later-sliced component to the earlier-sliced part.

Algorithm

Defining a list first.
#Use slicing method.
#在右旋和左旋後列印每個清單。

文法

FOR SLICING

#左旋轉 -

list_1 = list_1[3:] + list_1[:3]

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#右旋轉 -

list_1 = list_1[-3:] + list_1[:-3]

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Example

The following program rearranges the elements of a list. The original list is [11, 34, 26, 57, 92]. First rotate 3 units to the left. That is, the first three elements are moved to the end, the first three elements are moved to the end, resulting in [57, 92, 11, 34, 26]. Then rotate right by 3 so the last three elements move back and forth to their original positions [11,34,26,57,92].

接著向右旋轉2次，使最後兩個元素向前移動，得到 [26, 57, 92, 11, 34]。最後向左旋轉1次，將一個元素從開頭移到結尾，得到 [57, 92, 11, 34, 26]。

list_1 = [11, 34, 26, 57, 92]
print (" Primary list : " + str(list_1))
list_1 = list_1[3:] + list_1[:3]
print ("Output of the list after left rotate by 3 : " + str(list_1))
list_1 = list_1[-3:] + list_1[:-3]
print ("Output of the list after right rotate by 3(back to Primary list) : "+str(list_1))
list_1 = list_1[-2:] + list_1[:-2]
print ("Output of the list after right rotate by 2 : "+ str(list_1))
list_1 = list_1[1:] + list_1[:1]
print ("Output of the list after left rotate by 1 : " + str(list_1))

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輸出

Primary list : [11, 34, 26, 57, 92]
Output of the list after left rotate by 3 : [57, 92, 11, 34, 26]
Output of the list after right rotate by 3(back to Primary list) : [11, 34, 26, 57, 92]
Output of the list after right rotate by 2 : [57, 92, 11, 34, 26]
Output of the list after left rotate by 1 : [92, 11, 34, 26, 57]

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Using The Numpy Module

使用給定的軸，我們也可以使用python中的numpy.roll模組來旋轉清單中的元素。輸入數組的元素會因此被移動。如果一個元素從第一個位置移動到最後一個位置，它會回到初始位置。

Algorithm

導入numpy.roll模組
Define the list and give the particular index.
Print the output list.

Example

A list 'number' is created and assigned the values 1, 2, 4, 10, 18 and 83. The variable i is set to 1. The np.roll()

function from the NumPy library is then used on the list number with an argument of i which shifts each element in the list by 1 index position (the first element becomes last).

import numpy as np
if __name__ == '__main__':
   number = [1, 2, 4, 10, 18, 83]
   i = 1
   x = np.roll(number, i)
   print(x)

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輸出

[83 1 2 4 10 18]

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Usingcollections.deque.rotate()

rotate()函數是由collections模組中的deque類別提供的內建函數，用於實現旋轉操作。儘管不太為人所知，但這個函數更加實用。

Algorithm

首先從collection模組匯入deque類別。
定義一個列表
#列印主要清單
#使用rotate()函數旋轉元素
Print the output.

Example

The following program uses the deque data structure from the collections module to rotate a list. The original list is printed, then it rotates left by 3 and prints out the new rotated list. It then rotates right to position ) by 3 and prints out the resulting list.

from collections import deque
list_1 = [31, 84, 76, 97, 82]
print ("Primary list : " + str(list_1))
list_1 = deque(list_1)
list_1.rotate(-3)
list_1 = list(list_1)
print ("Output list after left rotate by 3 : " + str(list_1))
list_1 = deque(list_1)
list_1.rotate(3)
list_1 = list(list_1)
print ("Output list after right rotate by 3(back to primary list) : "+ str(list_1))

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輸出

Primary list : [31, 84, 76, 97, 82]
Output list after left rotate by 3 : [97, 82, 31, 84, 76]
Output list after right rotate by 3(back to primary list) : [31, 84, 76, 97, 82]

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結論

在本文中，我們簡要地解釋了四種不同的方法來旋轉清單中的元素。 ###

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