我有一个384MB的文本文件,里面有5000万行。每行包含两个用空格隔开的整数:一个键和一个值。该文件按键排序。我需要在Python中查找大约200个键的值的有效方法。
我的当前方法如下所示。它需要30秒钟。肯定有更有效率的Python解决方案,可以将这个时间缩短到最多几秒钟。
# list contains a sorted list of the keys we need to lookup
# there is a sentinel at the end of list to simplify the code
# we use pointer to iterate through the list of keys
for line in fin:
line = map(int, line.split())
while line[0] == list[pointer].key:
list[pointer].value = line[1]
pointer += 1
while line[0] > list[pointer].key:
pointer += 1
if pointer >= len(list) - 1:
break # end of list; -1 is due to sentinel
编写了二分查找+搜索解决方案(感谢kigurai!):
entries = 24935502 # number of entries
width = 18 # fixed width of an entry in the file padded with spaces
# at the end of each line
for i, search in enumerate(list): # list contains the list of search keys
left, right = 0, entries-1
key = None
while key != search and left <= right:
mid = (left + right) / 2
fin.seek(mid * width)
key, value = map(int, fin.readline().split())
if search > key:
left = mid + 1
else:
right = mid - 1
if key != search:
value = None # for when search key is not found
search.result = value # store the result of the search