Devon,
That 0-1 fraction method is a really nice way to generate lots of sets of 6
random integers 1-70 that sum to 172.
That got me to thinking -- shouldn't we be able to make all the generated
6-integer sets sum to 172?
f01=. 1e5 6?@$0 NB. Generating the fractions
NB. Now if we instument your verb a bit more:
itt1=. f01#~c=.172=+/"1 b=.([: <. 0.5 + ] * 172 % +/"1)"1 ] f01
$itt1
55085 6
NB. Not bad. Over half of the strings sum to 172.
NB. What about the other half (invert the c selection vector)?
5{.b#~-.c
42 23 5 20 41 40
50 35 50 8 19 11
37 34 34 17 22 27
49 10 25 2 34 53
30 14 44 15 32 38
How far off are the rest of these strings ?
d=.172-+/"1 b#~-.-.c
20{.d
1 _1 1 _1 _1 _1 1 1 _1 1 1 _1 1 1 1 1 1 1 _1 1
_20{.d
1 1 _1 _1 1 1 _1 _1 _1 _1 _1 1 _1 2 _2 1 1 _1 _1 1
>./d
2
<./d
_2
NB. Looks like the rest of the strings are off by as much as +/- 2
So we should be able find the discrepancy in the remaining strings, and
randomly pick one or more of the integers in each of the strings to add or
subtract 1 or 2 to. Then all the strings will sum to 172.
I'll leave that exercise to the reader...
Skip
Skip Cave
Cave Consulting LLC
On Wed, Jun 27, 2018 at 10:27 AM Devon McCormick <devon...@gmail.com> wrote:
> You could do it this way:
>
> itt=. 1e5 6?@$0 NB. Generate 6 columns of numbers between 0 and 1
> NB. Multiply by scaling factor to force sum to 172, then round and
> NB. select those that sum to 172 after rounding.
> itt=. itt#~172=+/"1 ([: <. 0.5 + ] * 172 % +/"1)"1 ] itt
> 3{.itt=. <.0.5+itt*("1 0)172%+/"1 itt
> 30 62 7 22 50 1
> 35 32 24 34 27 20
> 21 39 1 14 43 54
>
> NB. Remove any row with element not less than or equal to 70:
> $itt=. itt#~*./"1 itt<:70
> 52205 6
>
> So, over half of our random selections can be made to work.
>
> On Wed, Jun 27, 2018 at 2:24 AM, Skip Cave <s...@caveconsulting.com>
> wrote:
>
> > Raul, Robert, Jimmy, Louis, Bo, Rob,
> > Thanks so much for all the thoughtful and interesing answers. Your
> examples
> > gave me much insight on how the while. do. control structures work,
> which I
> > can never seem to remember. I also got a better understanding of
> > itemize/laminate, very useful for sticking vectors together.
> >
> > In my particular case. I didn't have to generate millions of
> combinations,
> > so efficiency wasn't much of an issue for me.
> >
> > Skip
> >
> >
> > On Tue, Jun 26, 2018 at 9:12 AM Skip Cave <s...@caveconsulting.com>
> wrote:
> >
> > > I want to generate n sets of 6 random integers from 1->70 where each
> set
> > > of 6 integers sums to 172
> > >
> > > Here's my first try:
> > >
> > > ts =: 3 : 0
> > >
> > > b=: 2 6$0
> > >
> > > for. i.y do. a=:1+6?70
> > >
> > > b=:b,a
> > >
> > > end.
> > >
> > > b#~172=+/"1 b
> > >
> > > )
> > >
> > > Test it:
> > >
> > > ts 1000
> > >
> > > 27 60 5 24 53 3
> > >
> > > 38 35 3 15 57 24
> > >
> > > 16 29 19 50 4 54
> > >
> > > This generates some 6-element vectors that sum to 172 by elimination,
> but
> > > I don't have control of how many vectors it produces.
> > >
> > >
> > > I want to change the logic in the loop so that it keeps generating sets
> > of
> > > 6 random integers, testing whether they sum to 172, saving just the
> sets
> > > that sum to 172, until I have saved y random sets that sum to 172, and
> > then
> > > exits.
> > >
> > >
> > > Any help would be appreciated.
> > >
> > >
> > > Skip
> > >
> > >
> > > Skip Cave
> > > Cave Consulting LLC
> > >
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
>
>
>
> --
>
> Devon McCormick, CFA
>
> Quantitative Consultant
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
----------------------------------------------------------------------
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