識別兩個連續的相同行並替換第一行

Question

我有以下輸入文件結構，每行上都有文本：

line1
line2
line3
line3
line4
line5
line6

當兩行完全相同時，即第3行，我要保留第二行，並將第一行的內容更改為“ SECTION MISSING”。 我沒有把它放在正確的位置。 我最接近的是下面的代碼，但是我得到的輸出是：

line1
line2
line3
SECTION MISSING
line4
etc.

當我想要時：

line1
line2
SECTION MISSING
line3 
line4

碼：

def uniq(iterator):
    previous = float("NaN")  # Not equal to anything
    section=("SECTION : MISSING\n")
    for value in iterator:
        if previous == value:
            yield section
        else:
            yield value
            previous = value
    return;

 with open('infile.txt','r') as file:
    with open('outfile.txt','w') as f:
        for line in uniq(file):
            f.write(line)

Answer 1

我認為您想產生previous value ，而不是value ：

def uniq(iterator):
    previous = None
    section = ("SECTION : MISSING\n")
    for value in iterator:
        if previous == value:
            yield section
        elif previous is not None:
            yield previous
        previous = value
    if previous is not None:
        yield previous

用法示例：

>>> list(uniq([1, 2, 2, 3, 4, 5, 6, 6]))
[1, 'SECTION : MISSING\n', 2, 3, 4, 5, 'SECTION : MISSING\n', 6]

Answer 2

就像是：

prev = None
with open('infile.txt','r') as fi:
    with open('outfile.txt','w') as fo:
        for line in fi:
            if prev is not None: 
                fo.write(prev if prev != line else "SECTION : MISSING\n")
            prev = line
        fo.write(prev)

將為您提供您要查找的輸出文件：

line1
line2
SECTION : MISSING
line3
line4
line5
line6

Answer 3

個人偏愛這些任務，我使用兩個游標而不是一個：

from itertools import tee, izip
with open(infile) as r, open(outfile, 'w') as w:
    p, c = tee(r)
    w.write(next(c))
    for prev,cur in izip(p,c):
        w.write(cur if prev!=cur else 'SECTION : MISSING\n')

Answer 4

如果你曾經有三個連續行（當然，兩個或兩個以上），您只需要更換的第一個，你可以用它來處理這種情況groupby ：

from itertools import groupby, islice, chain

def detect_missing(source):
    grouped = groupby(source)
    section = "SECTION: MISSING\n"
    for _, group in grouped:
        first_two = list(islice(group, 2))
        if len(first_two) > 1:
            first_two[0] = section
        yield from chain(first_two, group)

（Python 3，但是如果需要，您可以刪除yield from 。）