【python】リストについて

配列の特定の要素数をカウントする(Counter)

l = ['a', 'a', 'a', 'a', 'b', 'c', 'c']

print(l.count('a'))
# 4

print(l.count('b'))
# 1

print(l.count('c'))
# 2

print(l.count('d'))
# 0

配列の要素数をカウントする

l = ['a', 'a', 'a', 'a', 'b', 'c', 'c']

print(len(l))
# 7

配列(インデックス指定)の取り出し

sports = ["baseball","football","tennis"]

print(sports[0])
# baseball

print(sports[1])
# football

print(sports[2]) 
# tennis

print(sports[-1])
# tennis

要素の中身の総和

x = [0, 1, 2, 3, 4]

print(sum(x))
# 10

print(sum(x, 20))
# 30 ←総和＋20

要素の中身の総乗

import math

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

print(math.prod(a))
# 120

要素の中身の平均

import numpy

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

print(numpy.average(a))
# 2.5

配列に要素を追加する①(末尾)

l =　[0,1,2]

l.append(100)

print(l)
# [0, 1, 2, 100]


l.append('new')

print(l)
# [0, 1, 2, 100, 'new']


l.append([3, 4, 5])

print(l)
# [0, 1, 2, 100, 'new', [3, 4, 5]]

配列に要素を追加する②(指定位置)

l = list(range(3))

print(l)
# [0, 1, 2]


l.insert(0, 100)

print(l)
# [100, 0, 1, 2]


l.insert(-1, 200)

print(l)
# [100, 0, 1, 200, 2]


l.insert(0, [-1, -2, -3])

print(l)
# [[-1, -2, -3], 100, 0, 1, 200, 2]

配列に配列を連結する①

l = list(range(3))

print(l)
# [0, 1, 2]


l.extend([100, 101, 102])

print(l)
# [0, 1, 2, 100, 101, 102]


l.extend((-1, -2, -3))

print(l)
# [0, 1, 2, 100, 101, 102, -1, -2, -3]


l.extend('new')

print(l)
# [0, 1, 2, 100, 101, 102, -1, -2, -3, 'n', 'e', 'w']

配列に配列を連結する②

l2 = l + [5, 6, 7]

print(l2)
# [0, 1, 2, 100, 101, 102, -1, -2, -3, 'n', 'e', 'w', 5, 6, 7]


l += [5, 6, 7]

print(l)
# [0, 1, 2, 100, 101, 102, -1, -2, -3, 'n', 'e', 'w', 5, 6, 7]

配列に配列を挿入

l = list(range(3))

print(l)
# [0, 1, 2]


l[1:1] = [100, 200, 300]

print(l)
# [0, 100, 200, 300, 1, 2]


l = list(range(3))

print(l)
# [0, 1, 2]


l[1:2] = [100, 200, 300]

print(l)
# [0, 100, 200, 300, 2]

要素が２つ以上ない要素の数

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

print(l)
#["a","a","b","c","d"]

print(set(l))
#["b","c","d"]

print(len(set(l)))
#3