[R] trying to find the multiple combinations...

Bert Gunter bgunter.4567 at gmail.com
Sat Dec 9 16:58:44 CET 2017


Off topic, but for the record...

As Jeff already noted,the equation reduces to a single linear equation with
rational coefficients, so of course there are infinitely many integer
solutions.

Apologies for my dummheit.

-- Bert

On Fri, Dec 8, 2017 at 9:47 AM, Bert Gunter <bgunter.4567 at gmail.com> wrote:

> Please keep all replies onlist if there is no reason to keep them private.
> I am not a free, private consultant (and so might choose to ignore your
> followups); and I don't have all or necessarily the best answers anyway. So
> give yourself the maximal chance to be helped by others.
>
> Anyway,
>
> ?expand.grid is what you're looking for I think as an alternative to
> nested loops. If "results" is a vector of calculated results, i.e. the
> averages for the grid of combinations you generate, and "target" is your
> desired target (average), here of 15.0078, then
>
> which.min(abs(results - target))
> gives you the index of the closest results and
>
> abs(results - target) < tol
> gives you a vector of logicals of results that are within tol of the
> target.
>
> This is all pretty basic stuff, which suggests that you really need to
> spend some time with an R tutorial or two.  Here are some suggestions, but
> a web search would uncover many more, some of which might be more suitable
> for you:
> https://www.rstudio.com/online-learning/#R
>
> This list can help (not sure if I did here), but it cannot replace such
> homework on your own.
>
> Cheers,
> Bert
>
>
>
>
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along and
> sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
> On Fri, Dec 8, 2017 at 9:15 AM, Benjamin Sabatini <sunscape1 at hotmail.com>
> wrote:
>
>> Hi,
>>
>> Yes, actually, I could set an upper limit and grind through the
>> possibilities to find a minimal set or a few if that's what you mean. Close
>> to the result would be OK, too. Otherwise it would go on forever, I
>> suppose.
>>
>> At first I was thinking of just trying to write three for loops to test
>> for every set of the multiples of x, y, and z between something like 1 and
>> 10,000, but I understand that this is not at all efficient in R. So, (1*13.4689
>> + 1*12.85212+ 1*17.05071) / 1+1+1), (1*13.4689 + 2*12.85212+ 1*17.05071)
>> / 1+2+1)...
>>
>> Is there a better way? If I solve for z is it then easier with an upper
>> limit? So, z = x*0.753288 + y*1.0552
>> and then loop it?
>>
>> ------------------------------
>> *From:* Bert Gunter <bgunter.4567 at gmail.com>
>> *Sent:* Friday, December 8, 2017 3:16 PM
>> *To:* Jeff Newmiller
>> *Cc:* R-help; Benjamin Sabatini
>> *Subject:* Re: [R] trying to find the multiple combinations...
>>
>> Are x,y, and z supposed to be positive whole numbers? If so, there may be
>> no solutions. If there is a solution set, of course any multiple of the set
>> is a solution set, so presumably you want a minimal set in some sense. This
>> strikes me as a hard problem mathematically, but maybe there is some
>> obvious way to set an upper bound on a minimal x,y, and z, in which case a
>> simple grid search could then be used.
>>
>> Naturally, if any real numbers are sought, Jeff is correct.
>>
>> Cheers,
>> Bert
>>
>>
>>
>> Bert Gunter
>>
>> "The trouble with having an open mind is that people keep coming along
>> and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>>
>> On Fri, Dec 8, 2017 at 12:19 AM, Jeff Newmiller <jdnewmil at dcn.davis.ca.us
>> > wrote:
>>
>> Solve for one of your variables and it will be given in terms of the
>> other two. That is, there is a whole infinite plane of solutions. No,
>> aggregate will not be sufficient to enumerate the solution set..
>> --
>> Sent from my phone. Please excuse my brevity.
>>
>> On December 7, 2017 10:37:37 PM PST, Benjamin Sabatini <
>> sunscape1 at hotmail.com> wrote:
>> >Hi,
>> >
>> >I'm trying to find a way to determine what multiples of the combination
>> >of three or more numbers equals a forth number.
>> >
>> >So, if I had a number set like:
>> >
>> >c(13.4689, 12.85212, 17.05071)
>> >
>> >What combination and multiples of these numbers would average to
>> >15.0078? (so, something that would tell me x, y, and z in (x*13.4689 +
>> >y*12.85212+ z*17.05071) / x+y+z) = 15.0078
>> >
>> >I think this is doable with aggregate?
>> >
>> >       [[alternative HTML version deleted]]
>>
>> This is a plain text mailing list. Please learn how to use your email
>> program.
>>
>> >
>> >______________________________________________
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>> >and provide commented, minimal, self-contained, reproducible code.
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>>
>

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