How might I remove duplicate lines from a file?

On Unix/Linux, use the uniq command, as per David Locke's answer, or sort, as per William Pursell's comment.

If you need a Python script:

lines_seen = set() # holds lines already seen
outfile = open(outfilename, "w")
for line in open(infilename, "r"):
    if line not in lines_seen: # not a duplicate
        outfile.write(line)
        lines_seen.add(line)
outfile.close()

Update: The sort/uniq combination will remove duplicates but return a file with the lines sorted, which may or may not be what you want. The Python script above won't reorder lines, but just drop duplicates. Of course, to get the script above to sort as well, just leave out the outfile.write(line) and instead, immediately after the loop, do outfile.writelines(sorted(lines_seen)).

If you're on *nix, try running the following command:

sort <file name> | uniq

uniqlines = set(open('/tmp/foo').readlines())

this will give you the list of unique lines.

writing that back to some file would be as easy as:

bar = open('/tmp/bar', 'w').writelines(uniqlines)

bar.close()

get all your lines in the list and make a set of lines and you are done. for example,

>>> x = ["line1","line2","line3","line2","line1"]
>>> list(set(x))
['line3', 'line2', 'line1']
>>>

If you need to preserve the ordering of lines - as set is unordered collection - try this:

y = []
for l in x:
    if l not in y:
        y.append(l)

and write the content back to the file.

Look at script I created to remove duplicate emails from text files. Hope this helps!

# function to remove duplicate emails
def remove_duplicate():
    # opens emails.txt in r mode as one long string and assigns to var
    emails = open('emails.txt', 'r').read()
    # .split() removes excess whitespaces from str, return str as list
    emails = emails.split()
    # empty list to store non-duplicate e-mails
    clean_list = []
    # for loop to append non-duplicate emails to clean list
    for email in emails:
        if email not in clean_list:
            clean_list.append(email)
    return clean_list
    # close emails.txt file
    emails.close()
# assigns no_duplicate_emails.txt to variable below
no_duplicate_emails = open('no_duplicate_emails.txt', 'w')

# function to convert clean_list 'list' elements in to strings
for email in remove_duplicate():
    # .strip() method to remove commas
    email = email.strip(',')
    no_duplicate_emails.write(f"E-mail: {email}\n")
# close no_duplicate_emails.txt file
no_duplicate_emails.close()

edit it within the same file

lines_seen = set() # holds lines already seen

with open("file.txt", "r+") as f:
    d = f.readlines()
    f.seek(0)
    for i in d:
        if i not in lines_seen:
            f.write(i)
            lines_seen.add(i)
    f.truncate()

Readable and Concise

with open('sample.txt') as fl:
    content = fl.read().split('\n')

content = set([line for line in content if line != ''])

content = '\n'.join(content)

with open('sample.txt', 'w') as fl:
    fl.writelines(content)

cat <filename> | grep '^[a-zA-Z]+$' | sort -u > outfile.txt

To filter and remove duplicate values from the file.

Here is my solution

d = input("your file:") #write your file name here
file1 = open(d, mode="r")
file2 = open('file2.txt', mode='w')
file2 = open('file2.txt', mode='a')
file1row = file1.readline()


while file1row != "" :
    file2 = open('file2.txt', mode='a')
    file2read = open('file2.txt', mode='r')
    file2r = file2read.read().strip()
    if file1row not in file2r:
        file2.write(file1row)   
    file1row = file1.readline()
    file2read.close()
    file2.close