On 22.03.2021 23:14, Tim Menzies wrote:

given an array a[1]=10,a[2]=20,a[3]=30 anyone got an iterator that runs over all subsets. for example:

function show(lst) { print ""; for(i in lst ) print(i,lst[i]) }

forsubs("show", a) ==>

10

20

30

40

10, 20

10,30

20,30

10,20,30

(I suppose the "40" was a typo?)

As for a solution, with GNU awk where I can use bit-operations,
I might implement something like

function forsubs (a, n, m, z, w) {
n=length(a)
m=2^n
for (z=1; z<m; z++) {
w=1
for (y=1; y<m; y*=2) {
if (and(z,y)) printf " %s", a[w]
w++
}
printf "\n"
}
}
BEGIN { a[1]=10 ; a[2]=20 ; a[3]=30 ; forsubs(a) }

to create this output

10
20
10 20
30
10 30
20 30
10 20 30

The function relies on some properties (e.g. contiguous indices in a),
and to define another order of the resulting permutation you need some
tweaks.

Janis

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On 2021-03-22, Tim Menzies <[email protected]> wrote:

given an array a[1]=10,a[2]=20,a[3]=30 anyone got an iterator that runs over all subsets. for example:

The set of all subsets is the "power set". Is that what you mean?

The Rosetta Code site has solutions for calculating the power set in (at
the time of writing) 96 languages, including Awk

http://rosettacode.org/wiki/Power_Set#AWK

10

20

30

40

10, 20

10,30

20,30

10,20,30

The Rosetta Awk solution doesn't walk the subsets in this order,
unfortunately; if you need that, you have work to do.

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal

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On Monday, 22 March 2021 at 18:14:59 UTC-4, [email protected] wrote:

given an array a[1]=10,a[2]=20,a[3]=30 anyone got an iterator that runs over all subsets. for example:

function show(lst) { print ""; for(i in lst ) print(i,lst[i]) }

forsubs("show", a) ==>

10

20

30

40

10, 20

10,30

20,30

10,20,30

Two fun algorithms, given in C, C++, etc. Easy to Gawk.
iterative, using bits to filter output subsets, easy on memory https://www.geeksforgeeks.org/power-set/

recursive, 2^nth deep. Watch memory! https://www.geeksforgeeks.org/backtracking-to-find-all-subsets/

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

given an array a[1]=10,a[2]=20,a[3]=30 anyone got an iterator that runs over all subsets. for example:

function show(lst) { print ""; for(i in lst ) print(i,lst[i]) }

forsubs("show", a) ==>

10

20

30

40

10, 20

10,30

20,30

10,20,30

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)