Question

我是Python新手，已经花了很多时间解决这个问题，希望有人可以帮助我。我需要找到2个序列之间的重叠。重叠位于第一个序列的左端，第二个序列的右端。我希望函数找到重叠，并返回它。

我的序列是：

s1 = "CGATTCCAGGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTC"
s2 = "GGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTCGTCCAGACCCCTAGC"

我的功能应该命名为

def getOverlap(left, right)

s1为左序列，s2为正序。

结果应该是

‘GGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTC’

感谢任何帮助

Answer 1

您可以使用difflib.SequenceMatcher：

d = difflib.SequenceMatcher(None,s1,s2)
>>> match = max(d.get_matching_blocks(),key=lambda x:x[2])
>>> match
Match(a=8, b=0, size=39)
>>> i,j,k = match
>>> d.a[i:i+k]
'GGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTC'
>>> d.a[i:i+k] == d.b[j:j+k]
True
>>> d.a == s1
True
>>> d.b == s2
True

Answer 2

查看difflib库，更准确地说是find_longest_match()：

import difflib

def get_overlap(s1, s2):
    s = difflib.SequenceMatcher(None, s1, s2)
    pos_a, pos_b, size = s.find_longest_match(0, len(s1), 0, len(s2)) 
    return s1[pos_a:pos_a+size]

s1 = "CGATTCCAGGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTC"
s2 = "GGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTCGTCCAGACCCCTAGC"

print(get_overlap(s1, s2)) # GGCTCCCCACGGGGTACCCATAACTTGACAGTAGATCTC

Answer 3

Knuth-Morris-Pratt算法是一种很好的方法，可以在另一个内部找到一个字符串（因为我看到了DNA，我猜你想要扩展到......数十亿？）。

# Knuth-Morris-Pratt string matching
# David Eppstein, UC Irvine, 1 Mar 2002

from __future__ import generators

def KnuthMorrisPratt(text, pattern):

    '''Yields all starting positions of copies of the pattern in the text.
Calling conventions are similar to string.find, but its arguments can be
lists or iterators, not just strings, it returns all matches, not just
the first one, and it does not need the whole text in memory at once.
Whenever it yields, it will have read the text exactly up to and including
the match that caused the yield.'''

    # allow indexing into pattern and protect against change during yield
    pattern = list(pattern)

    # build table of shift amounts
    shifts = [1] * (len(pattern) + 1)
    shift = 1
    for pos in range(len(pattern)):
        while shift <= pos and pattern[pos] != pattern[pos-shift]:
            shift += shifts[pos-shift]
        shifts[pos+1] = shift

    # do the actual search
    startPos = 0
    matchLen = 0
    for c in text:
        while matchLen == len(pattern) or \
              matchLen >= 0 and pattern[matchLen] != c:
            startPos += shifts[matchLen]
            matchLen -= shifts[matchLen]
        matchLen += 1
        if matchLen == len(pattern):
            yield startPos

The link where I got the KMP python code（和内置，由于运行时常量，对于小问题会更快）。

对于前沿性能，使用字符串的前缀表和哈希窗口作为基本4整数（在生物学中，您将其称为k-mers或oligos）。 ; ）

祝你好运！

编辑：还有一个很好的技巧，你可以对第一个字符串中的每个前缀（总共n）和第二个字符串中的每个前缀（n个总和）进行排序。如果它们共享最大的公共子序列，则它们必须在排序列表中相邻，因此从排序列表中最接近的另一个字符串中查找该元素，然后获取完全匹配的最长前缀。：）

Answer 4

Longest Common Substring

def LongestCommonSubstring(S1, S2):
  M = [[0]*(1+len(S2)) for i in xrange(1+len(S1))]
  longest, x_longest = 0, 0
  for x in xrange(1,1+len(S1)):
    for y in xrange(1,1+len(S2)):
        if S1[x-1] == S2[y-1]:
            M[x][y] = M[x-1][y-1] + 1
            if M[x][y]>longest:
                longest = M[x][y]
                x_longest  = x
        else:
            M[x][y] = 0
  return S1[x_longest-longest: x_longest]

如何找到2个序列之间的重叠，并将其返回

4 个答案: