in reply to Sum of N elements in an M element array

This might help?
There are duplicates, eg 12 and 21. 
#!/usr/bin/perl
use strict;
use warnings;

my @perms = glob "{1,2,3}" x 3;
print "@perms\n";

@perms = glob "{1,2,3}" x 2;
print "@perms\n";

__END__
Prints:
111 112 113 121 122 123 131 132 133 211 212 213 221 222 223 231 232 23
+3 311 312 313 321 322 323 331 332 333

11 12 13 21 22 23 31 32 33

[download]
Another run:
#!/usr/bin/perl
use strict;
use warnings;

my @perms = glob "{a,b,c,d,e}" x 3;
print "@perms\n";
print "\n";


@perms = glob "{a,b,c,d,e}" x 2;
print "@perms\n";

__END__
Prints:
aaa aab aac aad aae aba abb abc abd abe aca acb acc acd ace ada adb ad
+c add ade aea aeb aec aed aee baa bab bac bad bae bba bbb bbc bbd bbe
+ bca bcb bcc bcd bce bda bdb bdc bdd bde bea beb bec bed bee caa cab 
+cac cad cae cba cbb cbc cbd cbe cca ccb ccc ccd cce cda cdb cdc cdd c
+de cea ceb cec ced cee daa dab dac dad dae dba dbb dbc dbd dbe dca dc
+b dcc dcd dce dda ddb ddc ddd dde dea deb dec ded dee eaa eab eac ead
+ eae eba ebb ebc ebd ebe eca ecb ecc ecd ece eda edb edc edd ede eea 
+eeb eec eed eee

aa ab ac ad ae ba bb bc bd be ca cb cc cd ce da db dc dd de ea eb ec e
+d ee

[download]

Replies are listed 'Best First'.
Re^2: Sum of N elements in an M element array
by LanX (Saint) on Feb 03, 2020 at 01:21 UTC
    For the record: your output is significantly different from others, because you allow single elements to appear multiple times, like in "aaa".

    The OP said "repetitions allowed", but I read this as the numbers don't need to be pairwise different.

    To increase the confusion does his demo not show any repetitions.

    > 

    ...
all possible 3 elements ;
a+b+c
a+b+d
a+b+e
...

    [download]

    slightly annoying.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
[d/l]
      Ok, I wanted to show the glob combination gizmo and the spec wasn't perfect.
      For permutations 3 of a set of 5, consider the following.
      No element is repeated, meaning no element of the input array appears more than once per "sum"
      I just sorted the output in my program editor rather than adding that feature to the Perl code. 
      #!/usr/bin/perl 
use strict;
use warnings;
use Algorithm::Permute;

my $p = Algorithm::Permute->new(['a','b','c','d','e'], 3);
 
while (my @res = $p->next) 
{
   print join("+", @res), "\n";
}
__END__
# I just used my editor to sort the output
# adapt the above code as you wish

a+b+c
a+b+d
a+b+e
a+c+b
a+c+d
a+c+e
a+d+b
a+d+c
a+d+e
a+e+b
a+e+c
a+e+d
b+a+c
b+a+d
b+a+e
b+c+a
b+c+d
b+c+e
b+d+a
b+d+c
b+d+e
b+e+a
b+e+c
b+e+d
c+a+b
c+a+d
c+a+e
c+b+a
c+b+d
c+b+e
c+d+a
c+d+b
c+d+e
c+e+a
c+e+b
c+e+d
d+a+b
d+a+c
d+a+e
d+b+a
d+b+c
d+b+e
d+c+a
d+c+b
d+c+e
d+e+a
d+e+b
d+e+c
e+a+b
e+a+c
e+a+d
e+b+a
e+b+c
e+b+d
e+c+a
e+c+b
e+c+d
e+d+a
e+d+b
e+d+c

      [download]
[reply]
[d/l]

        Whilst it is true that no element is repeated, for the purposes of the OP, this solution will produce multiple results for the same three elements being summed in a different order. Some form of filtering, perhaps involving a numerical sort of element numbers, a pack to a string and a grep with a %seen hash, would be required to remove duplicates.

        Update: Here's some code to show what I mean. All the faff with pack q{N*}, @{ $_ } is because we may be dealing with larger arrays where subscripts go into multiple digits. This code:-

        use 5.026;
use warnings;

use Algorithm::Permute;

my @arr  = ( 1, 2, 3, 4, 5 );
my $perm = Algorithm::Permute->new( [ 0 .. $#arr ], 3 );

my @allPerms;
while ( my @res = $perm->next() )
{
    push @allPerms, [ sort { $a <=> $b } @res ];
}

my @uniqPerms = do {
   my %seen;
   map  { [ unpack q{N*}, $_ ] }
   grep { ! $seen{ $_ } ++ }
   sort
   map  { pack q{N*}, @{ $_ } }
   @allPerms
   };

say join q{+}, @{ $_ } for @uniqPerms;

        [download]

        Produces:-

        0+1+2
0+1+3
0+1+4
0+2+3
0+2+4
0+3+4
1+2+3
1+2+4
1+3+4
2+3+4

        [download]

        Cheers,

        JohnGG

[reply]
[d/l]
[select]
Re^2: Sum of N elements in an M element array
by abhay180 (Sexton) on Feb 02, 2020 at 08:02 UTC
    Thanks Marshall. This helps. Never a great user of glob() function , will try it out.
[reply]
      This glob thing is a bit weird.
      Good Luck!
      Consider also: 
      #!/usr/bin/perl
use strict;
use warnings;

my @combos = glob "{a,b,c}{1,2}"; 
print "@combos\n";

__END__
Prints:
a1 a2 b1 b2 c1 c2

      [download]
[reply]
[d/l]

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