[英]how to retrieve string from a large file
我编写了一个代码,其中“IDS.txt”是一个制表符分隔文本文件,其中包含下面给出的ID,其中第一列表示ID第二个起始索引和第三列结束索引。
IDs.txt-------
“complete.txt”
我所给出的波纹管写剧本根据“IDs.txt”检索字符串片段它NOT
工作,请帮助我应该做出哪些改变来纠正码
with open("\Users\Zebrafish\Desktop\IDs.txt") as f: # will get input from the text
for line in f:
c = line.split("\t")
for i, x in enumerate(c): #passing values to start and end variables
if i == 1:
start = x
elif i == 2:
end = x
elif i == 0:
gene_name = x
infile = open("/Users/Zebrafish/Desktop/complete.txt") #file to get large string data
for seq in infile:
seqnew = seq.split("\t") # get data as single line
retrived = seqnew[int(start):int(end)] #retrieve fragment
print retrived
我不知道你为什么要在你的complete.txt
文件中拆分\\t
,这里是你的代码优化:
ids = {}
with open('/Users/Zebrafish/Desktop/ASHISH/IDs.txt') as f:
for line in f:
if len(line.strip()):
# This makes sure you skip blank lines
id,start,end = line.split('\t')
ids[id] = (int(start),int(end))
# Here, I assume your `complete.txt` is a file with one long line.
with open('/Users/Zebrafish/Desktop/ASHISH/complete.txt') as f:
sequence = f.readline()
# For each id, fetch the sequence "chunk:
for id,value in ids.iteritems():
start, end = value
print('{} {}'.format(id,sequence[start-1:end]))
3MB并不大(在可以运行Windows的计算机上)。 只需将第二个文件作为单个字符串加载到内存中,即可获取片段:
# populate `id -> (start, end)` map
ids = {}
with open(r"\Users\Zebrafish\Desktop\ASHISH\IDs.txt") as id_file:
for line in id_file:
if line.strip(): # non-blank line
id, start, end = line.split()
ids[id] = int(start), int(end)
# load the file as a single string (ignoring whitespace)
with open("/Users/Zebrafish/Desktop/ASHISH/complete.txt") as seq_file:
s = "".join(seq_file.read().split()) # or re.sub("\s+", "", seq_file.read())
# print fragments
for id, (start, end) in ids.items():
print("{id} -> {fragment}".format(id=id, fragment=s[start:end]))
如果complete.txt
文件不适合内存; 您可以使用mmap
,以字节序列的形式访问其内容,而无需将整个文件加载到内存中:
from mmap import ACCESS_READ, mmap
with open("complete.txt") as f, mmap(f.fileno(), 0, access=ACCESS_READ) as s:
# use `s` here (assume that indices refer to the raw file in this case)
# e.g., `fragment = s[start:end]`
删除行:
seqnew = seq.split("\t")
做就是了:
retrieved = seqnew[int(start):int(end)]
将获得您想要的子字符串。
那么你将能够:
print retrieved
谨防IDs.txt
中的领先\\t
>>> print "\ta\tb\tc"
a b c
>>> "\ta\tb\tc".split("\t")
['', 'a', 'b', 'c']
i == 0
是指空文本而不是基因ID。
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