Set Operations in the Unix Shell

Various Set operations are covered here, Hope you Enjoy.

Set Membership
--------------

$ grep -xc 'element' set    # outputs 1 if element is in set
                            # outputs >1 if set is a multi-set
                            # outputs 0 if element is not in set

$ grep -xq 'element' set    # returns 0 (true)  if element is in set
                            # returns 1 (false) if element is not in set

$ awk '$0 == "element" { s=1; exit } END { exit !s }' set
# returns 0 if element is in set, 1 otherwise.

$ awk -v e='element' '$0 == e { s=1; exit } END { exit !s }' set


Set Equality
------------

$ diff -q <(sort set1) <(sort set2) # returns 0 if set1 is equal to set2
                                    # returns 1 if set1 != set2

$ diff -q <(sort set1 | uniq) <(sort set2 | uniq)
# collapses multi-sets into sets and does the same as previous

$ awk '{ if (!($0 in a)) c++; a[$0] } END{ exit !(c==NR/2) }' set1 set2
# returns 0 if set1 == set2
# returns 1 if set1 != set2

$ awk '{ a[$0] } END{ exit !(length(a)==NR/2) }' set1 set2
# same as previous, requires >= gnu awk 3.1.5


Set Cardinality
---------------

$ wc -l set | cut -d' ' -f1    # outputs number of elements in set

$ wc -l < set

$ awk 'END { print NR }' set


Subset Test
-----------

$ comm -23 <(sort subset | uniq) <(sort set | uniq) | head -1
# outputs something if subset is not a subset of set
# does not putput anything if subset is a subset of set

$ awk 'NR==FNR { a[$0]; next } { if !($0 in a) exit 1 }' set subset
# returns 0 if subset is a subset of set
# returns 1 if subset is not a subset of set


Set Union
---------

$ cat set1 set2     # outputs union of set1 and set2
                    # assumes they are disjoint

$ awk 1 set1 set2   # ditto

$ cat set1 set2 ... setn   # union over n sets

$ cat set1 set2 | sort -u  # same, but assumes they are not disjoint

$ sort set1 set2 | uniq

$ sort -u set1 set2

$ awk '!a[$0]++'           # ditto


Set Intersection
----------------

$ comm -12 <(sort set1) <(sort set2)  # outputs insersect of set1 and set2

$ grep -xF -f set1 set2

$ sort set1 set2 | uniq -d

$ join <(sort -n A) <(sort -n B)

$ awk 'NR==FNR { a[$0]; next } $0 in a' set1 set2


Set Complement
--------------

$ comm -23 <(sort set1) <(sort set2)
# outputs elements in set1 that are not in set2

$ grep -vxF -f set2 set1           # ditto

$ sort set2 set2 set1 | uniq -u    # ditto

$ awk 'NR==FNR { a[$0]; next } !($0 in a)' set2 set1


Set Symmetric Difference
------------------------

$ comm -3 <(sort set1) <(sort set2) | sed 's/\t//g'
# outputs elements that are in set1 or in set2 but not both

$ comm -3 <(sort set1) <(sort set2) | tr -d '\t'

$ sort set1 set2 | uniq -u

$ cat <(grep -vxF -f set1 set2) <(grep -vxF -f set2 set1)

$ grep -vxF -f set1 set2; grep -vxF -f set2 set1

$ awk 'NR==FNR { a[$0]; next } $0 in a { delete a[$0]; next } 1;
       END { for (b in a) print b }' set1 set2


Power Set
---------

$ p() { [ $# -eq 0 ] && echo || (shift; p "$@") |
        while read r ; do echo -e "$1 $r\n$r"; done }
$ p `cat set`

# no nice awk solution, you are welcome to email me or put the comment.


Set Cartesian Product
---------------------

$ while read a; do while read b; do echo "$a, $b"; done < set1; done < set2

$ awk 'NR==FNR { a[$0]; next } { for (i in a) print i, $0 }' set1 set2


Disjoint Set Test
-----------------

$ comm -12 <(sort set1) <(sort set2)  # does not output anything if disjoint

$ awk '++seen[$0] == 2 { exit 1 }' set1 set2 # returns 0 if disjoint
                                             # returns 1 if not


Empty Set Test
--------------

$ wc -l set | cut -d' ' -f1 # outputs 0  if the set is empty
                            # outputs >0 if the set is not empty

$ wc -l < set           

$ awk '{ exit 1 }' set   # returns 0 if set is empty, 1 otherwise


Minimum
-------

$ head -1 <(sort set)    # outputs the minimum element in the set

$ awk 'NR == 1 { min = $0 } $0 < min { min = $0 } END { print min }'


Maximum
-------

$ tail -1 <(sort set)    # outputs the maximum element in the set

$ awk 'NR == 1 { max = $0 } $0 > max { max = $0 } END { print max }'