Diff for "BashFAQ/036"

Differences between revisions 1 and 10 (spanning 9 versions)

How can I get all lines that are: in both of two files (set intersection) or in only one of two files (set subtraction).

Use the comm(1) command:

# Bash
# intersection of file1 and file2
comm -12 <(sort file1) <(sort file2)
# subtraction of file1 from file2
comm -13 <(sort file1) <(sort file2)

Read the comm manpage for details.

If for some reason you lack the core comm program, you can use these other methods:

An amazingly simple and fast implementation, that took just 20 seconds to match a 30k line file against a 400k line file for me.
```
  # intersection of file1 and file2
  grep -xF -f file1 file2
  # subtraction of file1 from file2
  grep -vxF -f file1 file2
```
- It has grep read one of the sets as a pattern list from a file (-f), and interpret the patterns as plain strings not regexps (-F), matching only whole lines (-x).
- Note that the file specified with -f will be loaded into memory, so it doesn't scale for very large files.
- It should work with any POSIX grep; on older systems you may need to use fgrep rather than grep -F.

An implementation using sort and uniq:

  # intersection of file1 and file2
  sort file1 file2 | uniq -d  (Assuming each of file1 or file2 does not have repeated content)
  # file1-file2 (Subtraction)
  sort file1 file2 file2 | uniq -u
  # same way for file2 - file1, change last file2 to file1
  sort file1 file2 file1 | uniq -u

Another implementation of subtraction:
```
  sort file1 file1 file2 | uniq -c |
  awk '{ if ($1 == 2) { $1 = ""; print; } }'
```
- This may introduce an extra space at the start of the line; if that's a problem, just strip it away.
- Also, this approach assumes that neither file1 nor file2 has any duplicates in it.
- Finally, it sorts the output for you. If that's a problem, then you'll have to abandon this approach altogether. Perhaps you could use awk's associative arrays (or perl's hashes or tcl's arrays) instead.

These are subtraction and intersection with awk, regardless of whether the input files are sorted or contain duplicates:

  # prints lines only in file1 but not in file2. Reverse the arguments to get the other way round
  awk 'NR==FNR{a[$0];next} !($0 in a)' file2 file1

  # prints lines that are in both files; order of arguments is not important
  awk 'NR==FNR{a[$0];next} $0 in a' file1 file2

CategoryShell

-  ⇤ ← Revision 1 as of 2007-05-02 23:25:20 → 
  Size: 1960
  Editor: redondos
  Comment:
+   ← Revision 10 as of 2010-06-25 20:06:53 → ⇥
  Size: 2531
  Editor: MatthiasPopp
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-[[Anchor(faq36)]]
+<<Anchor(faq36)>>
 Line 3:
-Use the comm(1) command.
+Use the `comm(1)` command:
-Line 7:
+Line 6:
-  # intersection of file1 and file2
  comm -12 <(sort file1) <(sort file2)
  # subtraction of file1 from file2
  comm -13 <(sort file1) <(sort file2)
+# Bash
# intersection of file1 and file2
comm -12 <(sort file1) <(sort file2)
# subtraction of file1 from file2
comm -13 <(sort file1) <(sort file2)
 Line 13:
-Read the comm(1) manpage for details.
+Read the `comm` manpage for details.
 Line 15:
-If for some reason you lack the core comm(1) program, you can use these other methods:
+If for some reason you lack the core `comm` program, you can use these other methods:
 Line 17:
-an amazingly simple and fast implementation, that took just 20 seconds to match a 30k line file against a 400k line file for me.

note that it probably only works with GNU grep, and that the file specified with -f is will be loaded into ram, so it doesn't scale for very large files.

it has grep read one of the sets as a pattern list from a file (-f), and interpret the patterns as plain strings not regexps (-F), matching only whole lines (-x).

{{{
+. An amazingly simple and fast implementation, that took just 20 seconds to match a 30k line file against a 400k line file for me.
 {{{
-Line 26:
+Line 21:
-  # substraction of file1 from file2
  grep -vxF -f file1 file2
}}}
+  # subtraction of file1 from file2
  grep -vxF -f file1 file2}}}
-Line 30:
+Line 24:
-an implementation using sort and uniq
+  * It has grep read one of the sets as a pattern list from a file (-f), and interpret the patterns as plain strings not regexps (-F), matching only whole lines (-x).
  * Note that the file specified with -f will be loaded into memory, so it doesn't scale for very large files.
  * It should work with any POSIX grep; on older systems you may need to use `fgrep` rather than `grep -F`.
-Line 32:
+Line 28:
-{{{
+. An implementation using sort and uniq:
 {{{
-Line 38:
+Line 35:
-  sort file1 file2 file1 | uniq -u
}}}
+  sort file1 file2 file1 | uniq -u}}}
-Line 41:
+Line 37:
-another implementation of substraction:
{{{
  cat file1 file1 file2 | sort | uniq -c |
  awk '{ if ($1 == 2) { $1 = ""; print; } }'
}}}
+. Another implementation of subtraction:
 {{{
  sort file1 file1 file2 | uniq -c |
  awk '{ if ($1 == 2) { $1 = ""; print; } }'}}}
-Line 47:
+Line 42:
-This may introduce an extra space at the start of the line; if that's a problem, just strip it away.
+  * This may introduce an extra space at the start of the line; if that's a problem, just strip it away.
  * Also, this approach assumes that neither file1 nor file2 has any duplicates in it.
  * Finally, it sorts the output for you.  If that's a problem, then you'll have to abandon this approach altogether.  Perhaps you could use awk's associative arrays (or perl's hashes or tcl's arrays) instead.
-Line 49:
+Line 46:
-Also, this approach assumes that neither file1 nor file2 has any duplicates in it.
+. These are subtraction and intersection with awk, regardless of whether the input files are sorted or contain duplicates:
 {{{
  # prints lines only in file1 but not in file2. Reverse the arguments to get the other way round
  awk 'NR==FNR{a[$0];next} !($0 in a)' file2 file1
 Line 51:
-Finally, it sorts the output for you.  If that's a problem, then you'll have to abandon this approach altogether.  Perhaps you could use awk's associative arrays (or perl's hashes or tcl's arrays) instead.
+  # prints lines that are in both files; order of arguments is not important
  awk 'NR==FNR{a[$0];next} $0 in a' file1 file2 }}}


See also: http://www.pixelbeat.org/cmdline.html#sets

----
CategoryShell