Compare two files: lines present in one, not in the other, by one column comparison

Question

I need to compare 2 files. Column 1 is the same in both files. Column 2 is what I want to compare: I want all lines in file 1 that are not in file 2 when comparing column 2. Column 3 is different in both files, even for lines where column 1 and 2 are identical. I cannot remove column 3, because as an output I want the lines from file 1 including this column.

Here is an example:

File 1

21  12340   3
21  12341   7
21  12342   2
21  12343   89
21  12349   7

File 2

21  12340   55
21  12341   7
21  12343   89
21  12344   7
21  12346   88
21  12347   3
21  12348   37

My output would be:

21  12342   2
21  12349   7

Answer 1

One awk solution:

awk '
    FNR == NR {
        data[ $2 ] = 1;
        next;
    }
    FNR < NR {
        if ( ! ($2 in data) ) {
            print $0;
        }
    }
' file2 file1

Result:

21  12342   2
21  12349   7

Answer 2

join requires that the files be presorted, as they are in the esample's args to join), so if you need to manintain the sequence ot the output, it would need different approach. Note, it doesn't try to keep the width of the original field spacing.

join -1 2 -2 2 -v 1 <(sort file1) <(sort file2) | awk '{print  $2,$1,$3}'

output

21 12342 2
21 12349 7

Answer 3

Using egrep and awk:

egrep -v -f <(awk '{printf "^%s[ ]+%s[ ]+\n", $1, $2}' file2) file1

The awk bit inside <() generates patterns based on the contents of file2. The egrep uses these patterns to match lines in file1, with -v inverting the matching, printing only the lines that don't match.

Answer 4

Using Python from the bash shell:

paddy$ python -c 'import sys
with open(sys.argv[2]) as f: file2col2 = {line.split()[1] for line in f}
with open(sys.argv[1]) as f: print("".join(line for line in f 
                                           if line.split()[1] not in file2col2))
' file1.tmp file2.tmp
21  12342   2
21  12349   7

paddy$