for 使用前一项循环遍历 stdin

Question

我想比较一行与上一行而不在内存中存储任何内容（没有字典）。

示例数据：

a   2
file    1
file    2
file    4
for 1
has 1
is  2
lines   1
small   1
small   2
test    1
test    2
this    1
this    2
two 1

伪代码：

for line in sys.stdin:
    word, count = line.split()
    if word == previous_word:
        print(word, count1+count2)

我知道我会在数组上使用 enumerate 或 dict.iteritems 但我不能在 sys.stdin.

期望的输出：

a   2
file    7
for 1
has 1
is  2
lines   1
small   3
test    3
this    3
two 1

Answer 1

I would like to compare a line to the previous one without storing anything in memory (no dictionaries).

为了能够对所有具有相似词的前面行的计数求和，您需要维护一些状态。

通常这份工作适合awk。你可以考虑这个命令：

awk '{a[] += } p && p != {print p, a[p]; delete a[p]} {p = } 
END { print p, a[p] }' file

a 2
file 7
for 1
has 1
is 2
lines 1
small 3
test 3
this 3
two 1

使用delete，此解决方案不会将整个文件存储在内存中。仅在处理具有相同第一个字的行时保持状态。

Awk 参考资料：

Answer 2

基本逻辑是跟踪前一个单词。如果当前单词匹配，则累加计数。如果不是，则打印前一个单词及其计数，然后重新开始。有一些特殊的代码来处理第一次和最后一次迭代。

stdin_data = [
    "a   2",
    "file    1",
    "file    2",
    "file    4",
    "for 1",
    "has 1",
    "is  2",
    "lines   1",
    "small   1",
    "small   2",
    "test    1",
    "test    2",
    "this    1",
    "this    2",
    "two 1",
]  

previous_word = ""
word_ct = 0

for line in stdin_data:
    word, count = line.split()
    if word == previous_word:
        word_ct += int(count)
    else:
        if previous_word != "":
            print(previous_word, word_ct)
        previous_word = word
        word_ct = int(count)

# Print the final word and count
print(previous_word, word_ct)

输出：

a 2
file 7
for 1
has 1
is 2
lines 1
small 3
test 3
this 3
two 1

Answer 3

您的代码就快完成了。虽然不想将整个内容存储在内存中是值得称赞的，但您将不得不存储上一行的累积组件：

prev_word, prev_count = '', 0
for line in sys.stdin:
    word, count = line.split()
    count = int(count)
    if word == prev_word:
        prev_count += count
    elif prev_count:
        print(prev_word, prev_count)
        prev_word, prev_count = word, count

for 使用前一项循环遍历 stdin

for loop through stdin using previous item

python

bash

stdin

sys