通过仅更改一个字符的Python行进行迭代

Question

I have a file that looks like this

N1 1.023 2.11 3.789 

Cl1 3.124 2.4534 1.678

Cl2 # # #

Cl3 # # #

Cl4

Cl5

N2

Cl6

Cl7

Cl8

Cl9

Cl10

N3

Cl11


Cl12

Cl13

Cl14

Cl15

The three numbers continue down throughout.

What I would like to do is pretty much a permutation. These are 3 data sets, set 1 is N1-Cl5, 2 is N2-Cl10, and set three is N3 - end.

I want every combination of N's and Cl's. For example the first output would be

Cl1

N1

Cl2

then everything else the same. the next set would be Cl1, Cl2, N1, Cl3...and so on.

I have some code but it won't do what I want, becuase it would know that there are three individual data sets. Should I have the three data sets in three different files and then combine, using a code like:

list1 = ['Cl1','Cl2','Cl3','Cl4', 'Cl5']

for line in file1:
    line.replace('N1', list1(0))
    list1.pop(0)
    print >> file.txt, line,

or is there a better way?? Thanks in advance

Answer 1

This should do the trick:

from itertools import permutations

def print_permutations(in_file):
    separators = ['N1', 'N2', 'N3']
    cur_separator = None
    related_elements = []

    with open(in_file, 'rb') as f:
        for line in f:
            line = line.strip()

            # Split Nx and CIx from numbers.
            value = line.split()[0]

            # Found new Nx. Print previous permutations.
            if value in separators and related_elements:
                for perm in permutations([cur_separator] + related_elements)
                    print perm
                cur_separator = line
                related_elements = []
            else:
                # Found new CIx. Append to the list.
                related_elements.append(value)

Answer 2

You could use regex to find the line numbers of the "N" patterns and then slice the file using those line numbers:

import re
n_pat = re.compile(r'N\d')
N_matches = []
with open(sample, 'r') as f:
    for num, line in enumerate(f):
        if re.match(n_pat, line):
            N_matches.append((num, re.match(n_pat, line).group()))

>>> N_matches
[(0, 'N1'), (12, 'N2'), (24, 'N3')]

After you figure out the line numbers where these patterns appear, you can then use itertools.islice to break the file up into a list of lists:

import itertools

first = N_matches[0][0]
final = N_matches[-1][0]
step = N_matches[1][0]
data_set = []
locallist = []

while first < final + step:
    with open(file, 'r') as f:
        for item in itertools.islice(f, first, first+step):
            if item.strip():
                locallist.append(item.strip())
        dataset.append(locallist)
        locallist = []
    first += step

itertools.islice is a really nice way to take a slice of an iterable. Here's the result of the above on a sample:

>>> dataset

[['N1 1.023 2.11 3.789', 'Cl1 3.126 2.6534 1.878', 'Cl2 3.124 2.4534 1.678', 'Cl3 3.924 2.1134 1.1278', 'Cl4', 'Cl5'], ['N2', 'Cl6 3.126 2.6534 1.878', 'Cl7 3.124 2.4534 1.678', 'Cl8 3.924 2.1134 1.1278', 'Cl9', 'Cl10'], ['N3', 'Cl11', 'Cl12', 'Cl13', 'Cl14', 'Cl15']]

After that, I'm a bit hazy on what you're seeking to do, but I think you want permutations of each sublist of the dataset? If so, you can use itertools.permutations to find permutations on various sublists of dataset:

for item in itertools.permutations(dataset[0]):
    print(item)
etc.

Final Note:

Assuming I understand correctly what you're doing, the number of permutations is going to be huge. You can calculate how many permutations there are them by taking the factorial of the number of items. Anything over 10 (10!) is going to produce over 3,000,000 million permutations.