比较列表中的字符串？

Question

我在一个列表中有一组字符串，该列表在下面的代码中给出。我想将每个字符串与其以前的字符串进行比较。显然，第一个定位的字符串不会与前一个字符串进行比较，因为没有任何字符串。逻辑基本上是： 第二个定位的字符串与第一个定位的字符串进行比较， 第 3 个定位字符串与第 1 个和第 2 个定位字符串进行比较， ... ...

s = ["avocado", "banana", "carrot", "avocado", "carrot", "grapes", "orange"]
for i in range(2,len(s)):
    for j in range(i,2, -1):
        if s[i] == s[j]:
            print (s[i])

现在，如果找到匹配项，将显示带有位置的字符串名称。如avocado found in position 4 and 1。 我被困在这段代码中。我应该如何进行？

Answer 1

另一种方法是您可以将项目的字典制作到位置

from collections import defaultdict

d = defaultdict(list)
for i in range(len(s)):
    d[s[i]].append(i + 1) # '+ 1' since we count from 1-index

for item, positions in d.items():
    if len(positions) > 1:
        print("{} found at positions {}".format(item, positions))

Answer 2

s = ["avocado", "banana", "carrot", "avocado", "carrot", "grapes", "orange"]
for i in range(1, len(s)):
    for j in range(i):
        if s[i] == s[j]:
            print(s[i])

你很亲密。使用 range(i) 从 0 计数到 i。使用索引 1 来获取列表中的第二项（列表从 0 开始）。

Answer 3

这似乎适合一般用例：

a = ['a','b','c','d','e','a','b','e','d']

for i in list(set(a)):
    b = [j for j, e in enumerate(a) if e == i]
    if len(b) > 1:
        print(i," found in positions:",b )

输出：

b  found in positions: [1, 6]
a  found in positions: [0, 5]
d  found in positions: [3, 8]
e  found in positions: [4, 7]

Answer 4

首先，您必须确定所有单词的位置，例如在字典里。然后你可以打印带有位置的单词：

from collections import defaultdict
positions = defaultdict(list)
s = ["avocado", "banana", "carrot", "avocado", "carrot", "grapes", "orange"]
for position, word in enumerate(s):
    positions[word].append(position)

for word, position in positions.items():
    print(f"{word} found at positions {' and '.join(position)}")

Answer 5

您可以使用 itertools 中的组合函数来有效地遍历所有对：

s = ["avocado", "banana", "carrot", "avocado", "carrot", "grapes", "orange"]
from itertools import combinations
matches = [(w1,p1,p2) for (p1,w1),(p2,w2) in combinations(enumerate(s),2) if w1==w2]
print("\n".join(f"{word} found in position {p1} and {p2}" for word,p1,p2 in matches))


# avocado found in position 0 and 3
# carrot found in position 2 and 4