列表的乐趣

littleGrow 发布于2019-07-24 17:49 / 566人阅读

摘要：列表的乐趣标签空格分隔文章的原文是删除元素所有等于值的元素重复警告该方法不负责列表项的顺序。

列表的乐趣

标签（空格分隔）： Python list

文章的原文是 Fun with Lists

1 删除元素 1.1 所有等于 X 值的元素

x = 4

a = [1, 2, 3, 4, 4, 5, 6, 1, 4]
for i in range(a.count(x)):
    a.pop(a.index(x))
print(a)

[1, 2, 3, 5, 6, 1]

a = [1, 2, 3, 4, 4, 5, 6, 1, 4]
b = [v for v in a if v != x]
print(b)
[1, 2, 3, 5, 6, 1]

print(a)
[1, 2, 3, 4, 4, 5, 6, 1, 4]

1.2 重复

警告!
该方法不负责列表项的顺序。

a = [1, 2, 3, 4, 3, 5, 1, 6]
b = list(set(a))
print(b)
[1, 2, 3, 4, 5, 6]

1.3 第一个元素

a = [1, 2, 3, 4, 5, 6]
b = a.pop(0)
print(b)
1

print(a)
[2, 3, 4, 5, 6]

a = [1, 2, 3, 4, 5, 6]
del a[0]
print(a)
[2, 3, 4, 5, 6]

a = [1, 2, 3, 4, 5, 6]
d = a[1:]
print(d)
[2, 3, 4, 5, 6]

print(a)
[1, 2, 3, 4, 5, 6]

1.4 最后一个元素

a = [1, 2, 3, 4, 5, 6]
b = a.pop()
print(b)
6

print(a)
[1, 2, 3, 4, 5]

a = [1, 2, 3, 4, 5, 6]
del a[-1]
print(a)
[1, 2, 3, 4, 5]

a = [1, 2, 3, 4, 5, 6]
c = a[:-1]
print(c)
[1, 2, 3, 4, 5]

print(a)
[1, 2, 3, 4, 5, 6]

1.5 第 n 个元素

n = 3
a = [1, 2, 3, 4, 5, 6]
b = a.pop(n - 1)
print(b)
3

print(a)
[1, 2, 4, 5, 6]

a = [1, 2, 3, 4, 5, 6]
del a[n - 1]
print(a)
[1, 2, 4, 5, 6]

a = [1, 2, 3, 4, 5, 6]
c = a[:n - 1] + a[n:]
print(c)
[1, 2, 4, 5, 6]

print(a)
[1, 2, 3, 4, 5, 6]

a = [1, 2, 3, 4, 5, 6]
c = [v for i, v in enumerate(a) if i != n - 1]
print(c)
[1, 2, 4, 5, 6]

print(a)
[1, 2, 3, 4, 5, 6]

2 替换元素 2.1 所有等于 x 值的元素

x = 4

a = [1, 2, 3, 4, 4, 5, 6, 1, 4]
for i in range(a.count(x)):
    a[a.index(x)] = 0
print(a)
[1, 2, 3, 0, 0, 5, 6, 1, 0]

a = [1, 2, 3, 4, 4, 5, 6, 1, 4]
b = [v if v != x else 0 for v in a ]
print(b)
[1, 2, 3, 0, 0, 5, 6, 1, 0]
print(a)
[1, 2, 3, 4, 4, 5, 6, 1, 4]

2.2 第一个元素

a = [1, 2, 3, 4]
a[0] = 0
print(a)
[0, 2, 3, 4]

a = [1, 2, 3, 4]
b = [0] + a[1:]
print(b)
[0, 2, 3, 4]
print(a)
[1, 2, 3, 4]

2.3 最后一个元素

a = [1, 2, 3, 4]
a[-1] = 0
print(a)
[1, 2, 3, 0]

a = [1, 2, 3, 4]
b = a[:-1] + [0]
print(b)
[1, 2, 3, 0]
print(a)
[1, 2, 3, 4]

2.4 第 n 个元素

n = 3

a = [1, 2, 3, 4]
a[n - 1] = 0
print(a)
[1, 2, 0, 4]

a = [1, 2, 3, 4]
b = [v if i != n -1 else 0 for i, v in enumerate(a)]
print(b)
[1, 2, 0, 4]
print(a)
[1, 2, 3, 4]

3 排序 3.1 按照字母顺序排列地 (不分大小写)

a = ["d", "C", "B", "a"]

b = sorted(a, key=lambda x: x.lower())
print(b)
["a", "B", "C", "d"]
print(a)
["d", "C", "B", "a"]

a.sort(key=lambda s: s.lower())
print(a)
["a", "B", "C", "d"]

3.2 按照字母顺序排列地 (分大小写)

a = ["d", "C", "B", "a"]

b = sorted(a)
print(b)
["B", "C", "a", "d"]
print(a)
["d", "C", "B", "a"]

a.sort()
print(a)
["B", "C", "a", "d"]

3.3 升序

a = ["a", "c", "d", "b"]

b = sorted(a, reverse=True)
print(b)
["d", "c", "b", "a"]
print(a)
["a", "c", "d", "b"]

a.sort(reverse=True)
print(a)
["d", "c", "b", "a"]

3.4 根据字符串长度


a = ["aaaa", "B", "CCC", "dd"]

b = sorted(a, key=lambda x: len(x))
print(b)
["B", "dd", "CCC", "aaaa"]
print(a)
["aaaa", "B", "CCC", "dd"]

a.sort(key=lambda x: len(x))
print(a)
["B", "dd", "CCC", "aaaa"]

4 其他 4.1 列表中的所有值相加

a = [1, 2.5, 7, 13221, 4.6545]
b = sum(a)
print(b)
13236.1545

4.2 在列表中新增元素

a = [1, 2, 3]
a.append(4)
print(a)
[1, 2, 3, 4]

4.3 使函数对列表中的每个元素生效

def func(x):
    print(x)

def func_2(x):
    return 2*x

a = [1, 2, 3, 4]
map(func, a)
1
2
3
4

b = map(func_2, a)
print(b)
[2, 4, 6, 8]
c = [func_2(x) for x in a]
print(c)
[2, 4, 6, 8]

4.4 两个列表的笛卡尔积 (矢量)

a = [1, 2, 3]
b = [4, 5, 6]

c = [(x, y) for x in a for y in b]
print(c)
[(1, 4), (1, 5), (1, 6), (2, 4), (2, 5), (2, 6), (3, 4), (3, 5), (3, 6)]

import itertools
d = [p for p in itertools.product(a, b)]
print(d)
[(1, 4), (1, 5), (1, 6), (2, 4), (2, 5), (2, 6), (3, 4), (3, 5), (3, 6)]

4.5 n 个列表的笛卡尔积 (矢量)

from pprint import pprint
import itertools

a = [[0, 1], [2, 3], [4, 5]]

b = [p for p in itertools.product(*a)]

print(b)
[(0, 2, 4),
 (0, 2, 5),
 (0, 3, 4),
 (0, 3, 5),
 (1, 2, 4),
 (1, 2, 5),
 (1, 3, 4),
 (1, 3, 5)]

4.6 检查两个列表是否有一个共同的元素

a = [1, 2, 0]
b = [3, 0, 4]

d = len((set(a) & set(b))) > 0
print(d)
True

4.7 检查一个列表是否包含值 x

a = [1, 2.5, 7, 13221, 4.6545]
if 7 in a:
    print("yes")
else:
    print("no")
yes

4.8 计算 x 出现在一个列表中的次数

a = [1, 2.5, 7, 13221, 4.6545, 7]
b = a.count(7)
print(b)
2

4.9 两个列表的不同

a = [1, 2, 3, 4]
b = [3, 4, 5, 6]

c = [x for x in a if not x in b]
print(c)
[1, 2]

d = list(set(a) - set(b))
print(d)
[1, 2]

e = list(set.difference(set(a), set(b)))
print(e)
[1, 2]

4.10 n 个列表的不同


a = [1, 2, 3, 4]
b = [[3, 5, 6, 7], [1, 8, 9, 10]]

a - b[0] - b[1]:

c = [x for x in a if not any([x in l for l in b])]
print(c)
[2, 4]

d = list(set(a).difference(*[set(l) for l in b]))
print(d)
[2, 4]

4.11 一个列表中首先出现的 n 个元素

n = 2

a = [1, 2, 3, 4, 5, 6]
b = a[:2]
print(b)
[1, 2]

4.12 一个列表中首先出现的 n 个非 x 值的元素

n = 3
x = 2

a = [1, 2, 2, 3, 2, 2, 2, 4, 5, 6]

gen = (v for v in a if v != x)
b = [gen.next() for i in range(n)]
print(b)
[1, 3, 4]
c = []
for v in a:
    if v != x:
        c.append(v)
    if len(c) == n:
        break
print(c)
[1, 3, 4]
4.13   Flatten a list of lists

a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

b = [i for s in a for i in s]
print(b)
[1, 2, 3, 4, 5, 6, 7, 8, 9]

4.14 把 x 插入 y 第一次出现之后的位置

x = 4
y = 3
a = [1, 2, 3, 5, 3, 6, 2]

try:
    a.insert(a.index(y) + 1, x)
except ValueError:
    a.append(x)
print(a)
[1, 2, 3, 4, 5, 3, 6, 2]
a = [1, 2, 3, 5, 3, 6, 2]
try:
    i = a.index(y)
    b = a[:i + 1] + [x] + a[i + 1:]
except ValueError:
    b = a + [x]
print(b)
[1, 2, 3, 4, 5, 3, 6, 2]
print(a)
[1, 2, 3, 5, 3, 6, 2]

4.15 把 x 插入 y 第一次出现之前的位置

x = 3
y = 4
a = [1, 2, 4, 5, 4, 6, 2]

try:
    a.insert(a.index(y), x)
except ValueError:
    a.append(x)
print(a)
[1, 2, 3, 4, 5, 4, 6, 2]

a = [1, 2, 4, 5, 4, 6, 2]
try:
    i = a.index(y)
    b = a[:i] + [x] + a[i:]
except ValueError:
    b = a + [x]
print(b)
[1, 2, 3, 4, 5, 4, 6, 2]
print(a)
[1, 2, 4, 5, 4, 6, 2]

4.16 两个列表的相同元素

a = [1, 2, 3, 4]
b = [3, 4, 5, 6]

c = [x for x in a if x in b]
print(c)
[3, 4]
d = list(set(a) & set(b))
print(d)
[3, 4]
e = list(set(a).intersection(b))
print(e)
[3, 4]

4.17 n 个列表的相同元素

a = [[1, 2, 3, 4], [3, 4, 5, 6], [1, 3, 7, 8]]

b = list(set.intersection(*[set(l) for l in a]))
print(b)
[3]
c = [x for x in a[0] if all([x in l for l in a[1:]])]
print(c)
[3]

4.18 Iterate over every other element of a list

a = [1, 2, 3, 4, 5, 6]
for x in a[::2]:
    print x
1
3
5

4.19 遍历列表的索引/值对

a = [1, 2.5, 7, 13221, 4.6545]
for i, v in enumerate(a):
    print("%i: %i" % (i, v))
0: 1
1: 2
2: 7
3: 13221
4: 4

4.20 遍历一个列表的元素

a = [1, 2, 3, 4]
for x in a:
    print x
1
2
3
4

4.21 列表中最大的数

a = [1, 2.5, 7, 13221, 4.6545]
b = max(a)
print(b)
13221
4.22   Last n elements of a list

n = 2

a = [1, 2, 3, 4, 5, 6]
b = a[-2:]
print(b)
[5, 6]

4.23 一个列表的长度

a = [1, 2, 3, 4]
l = len(a)
print(l)
4

4.24 合并两个列表

a = [1, 2, 3]
b = [4, 5, 6]

c = a + b
print(c)
[1, 2, 3, 4, 5, 6]
print(a)
[1, 2, 3]
print(b)
[4, 5, 6]

a.extend(b)
print(a)
[1, 2, 3, 4, 5, 6]
print(b)
[4, 5, 6]

4.25 列表的组合

from pprint import pprint
from itertools import permutations as perm

a = ["a", "b", "c"]

b = list(perm(a))
pprint(b)
[("a", "b", "c"),
 ("a", "c", "b"),
 ("b", "a", "c"),
 ("b", "c", "a"),
 ("c", "a", "b"),
 ("c", "b", "a")]

c = ["".join(p) for p in perm(a)]
print(c)
["abc", "acb", "bac", "bca", "cab", "cba"]

d = ["".join(p) for p in perm(a, 2)]
print(d)
["ab", "ac", "ba", "bc", "ca", "cb"]

4.26 Prepend an element to a list

a = [2, 3, 4]

a.insert(0, 1)
print(a)
[1, 2, 3, 4]
a = [2, 3, 4]

b = [1] + a
print(b)
[1, 2, 3, 4]
print(a)
[2, 3, 4]

4.27 列表反序

a = [1, 2, 3, 4]
a.reverse()
print(a)
[4, 3, 2, 1]

a = [1, 2, 3, 4]
c = a[::-1]
print(c)
[4, 3, 2, 1]
print(a)
[1, 2, 3, 4]

4.28 列表中最小的数字

a = [1, 2.5, 7, 13221, 4.6545]
b = min(a)
print(b)
1

4.29 2 个列表的对称差

a = [1, 2, 3, 4]
b = [3, 4, 5, 6]

c = [x for x in a if x not in b] + [x for x in b if x not in a]
print(c)
[1, 2, 5, 6]

d = list(set(a) ^ set(b))
print(d)
[1, 2, 5, 6]

e = list(set(a).symmetric_difference(b))
print(e)
[1, 2, 5, 6]

4.30 n 个列表的对称差

a = [[1, 2, 3, 4], [3, 4, 5, 6], [1, 5, 7, 8]]

b = a[0]
for i in range(len(a) - 1):
    b = list(set(b) ^ set(a[i + 1]))
print(b)
[2, 6, 7, 8]
tmp = {}
for v in [i for s in a for i in s]:
    tmp[v] = (v not in tmp)
c = [k for k, v in tmp.iteritems() if v]
print(c)
[2, 6, 7, 8]

4.31 两个列表的交集

a = [1, 2, 3, 4]
b = [3, 4, 5, 6]

c = [x for x in set(a + b)]
print(c)
[1, 2, 3, 4, 5, 6]
d = list(set(a) | set(b))
print(d)
[1, 2, 3, 4, 5, 6]
e = list(set(a).union(b))
print(e)
[1, 2, 3, 4, 5, 6]

4.32 n 个列表的交集

a = [[1, 2, 3, 4], [3, 4, 5, 6], [1, 6, 7, 8]]

b = list(set.union(*[set(l) for l in a]))
print(b)
[1, 2, 3, 4, 5, 6, 7, 8]
import itertools
c = [x for x in set(itertools.chain(*a))]
print(c)
[1, 2, 3, 4, 5, 6, 7, 8]

4.33 列表的左边加 0

max_length = 10

a = [1, 2, 3, 4]

b = [0]*(max_length - len(a)) + a
print(b)
[0, 0, 0, 0, 0, 0, 1, 2, 3, 4]

4.34 列表的右边加 0

max_length = 10

a = [1, 2, 3, 4]

b = a + [0]*(max_length - len(a))
print(b)
[1, 2, 3, 4, 0, 0, 0, 0, 0, 0]

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