python，比较位于两个不同文本文件中的列中的字符串

Question

I have 2 text files, "animals.txt" and "colors.txt" as follows, where the 2 Strings in each row are separated by a tab.

"animals.txt"

12345  dog

23456  sheep

34567  pig

"colors.txt"

34567  pink

12345  black

23456  white

I want to write Python code that:

1. For every rows in "animals.txt" takes the string in the first column (12345, then 23456, then 34567)
2. Compares this string to the strings in the first column in "colors.txt"
3. If it finds a match (12345 == 12345, etc) , it writes two output files:

output1, containing the rows of animals.txt + the value in the second column of colors.txt that corresponds to the querying value (12345):

12345 dog   black
23456 sheep white
34567 pig   pink 

output2 containing a list of the values in the second column of colors.txt that correspond to the querying value (12345, then 23456, then 34567)):

black
white
pink

Answer 1

If order doesn't matter, this becomes a pretty easy problem:

with open('animals.txt') as f1, open('colors.txt') as f2:
    animals = {} 
    for line in f1:
        animal_id, animal_type = line.split('\t')
        animals[animal_id] = animal_type

    #animals = dict(map(str.split,f1)) would work instead of the above loop if there are no multi-word entries.

    colors={}
    for line in f2:
        color_id, color_name = line.split('\t')
        colors[color_id] = color_name

    #colors = dict(map(str.split,f2)) would work instead of the above loop if there are no multi-word entries.
    #Thanks @Sven for pointing this out.

common=set(animals.keys()) & set(colors.keys())  #set intersection. 
with open('output1.txt','w') as f1, open('output2.txt','w') as f2:
     for i in common:  #sorted(common,key=int) #would work here to sort.
         f1.write("%s\t%s\t%s\n"%(i,animals[i],colors[i])
         f2.write("%s"%colors[i])

You might be able to do this a little more elegantly via a defaultdict where you append to a list when a particular key is encountered, then when writing you test that the length of the list is 2 before you output, but, I'm not convinced that approach is better.

Answer 2

Do you need to use python? If you are using bash and your inputs are not sorted, do:

$ join -t $'\t' <( sort animals.txt ) <( sort colors.txt ) > output1
$ cut -f 3 output1 > output2

If you do not have a shell that supports process substitution, then sort your input files and do:

$ join -t '<tab>' animals.txt colors.txt > output1
$ cut -f 3 output1 > output2

Where <tab> is an actual tab character. Depending on your shell, you may be able to enter it with ctrl-V followed by a tab key. (Or use a different delimiter for cut.)

Answer 3

I would use pandas

animals, colors = read_table('animals.txt', index_col=0), read_table('colors.txt', index_col=0)
df = animals.join(colors)

results in:

animals.join(colors)
Out[73]: 
       animal  color
id
12345  dog     black
23456  sheep   white
34567  pig     pink

then to output color in order of id to file:

df.color.to_csv(r'out.csv', index=False)

if you are unable to add column headings to the textfile they can be added on import

animals = read_table('animals.txt', index_col=0, names=['id','animal'])

Answer 4

Under the assumption that each line in the input files is structured exactly as the examples:

with open("c:\\python27\\output1.txt","w") as out1, \ 
     open("c:\\python27\\output2.txt","w") as out2:

    for outline in [animal[0]+"\t"+animal[1]+"\t"+color[1] \
                    for animal in [line.strip('\n').split("\t") \
                    for line in open("c:\\python27\\animals.txt","r").readlines()] \
                    for color in [line.strip('\n').split("\t") \
                    for line in open("c:\\python27\\colors.txt","r").readlines()] \
                    if animal[0] == color[0]]:

        out1.write(outline+'\n')
        out2.write(outline[outline.rfind('\t')+1:]+'\n')

I think that would do it for you.

Perhaps not the most elegant/fast/clear method - but pretty short. Technically that's 4 lines, I believe.