Re: How to find the difference between two lists (opposite of union[]?)
- To: mathgroup at smc.vnet.net
- Subject: [mg119910] Re: How to find the difference between two lists (opposite of union[]?)
- From: Priyan Fernando <priyan.fernando at gmail.com>
- Date: Wed, 29 Jun 2011 05:28:42 -0400 (EDT)
This should work:
mList = RandomInteger[{1, 1000}, 1000] // Sort
entirerange = Range[1, 1000]
Complement[entirerange, mList]
We basically find the complement of your set of random numbers and the
entirerange(1...1000)
On 28 June 2011 17:25, McHale, Paul <Paul.McHale at excelitas.com> wrote:
> I have been working through a neat book called Mathematica(r): A
> Problem-Centered Approach<
> http://www.amazon.com/Mathematica%C2%AE-Problem-Centered-Approach-Undergraduate-Mathematics/dp/1849962502/ref=sr_1_2?ie=UTF8&qid=1309181549&sr=8-2>.
> I have a problem I would like to know if there is a more elegant solution.
> I would think involving set theory, but I can't seem to (embarrassingly)
> find it.
>
> I want to generate 1000 random integers between 1 and 1000. Then find out
> what numbers between 1 and 1000 were not generated.
>
> (* Generate random list of 1000 numbers with range 1-1000*)
> mList=RandomInteger[{1,1000},1000] //Sort;
>
> (* Find out what numbers were omitted in the range 1-1000*)
> (* Make a list of numbers 1-1000 with position of each within original
> array *)
> mList=Table[{i,Position[mList,i] //Flatten},{i,1,1000}];
>
> (* select numbers with no position in original array (musical chairs) *)
> Select[mList,Length[#[[2]]]==0&][[All,1]]
>
> This works creating a lot of extra array in the process. Just wanted to
> ask what are the methods you guys would use to solve this?
>
> A funny (non-working) way of stating the same thing would be:
>
> (* Generate random list of 1000 numbers with range 1-1000*)
> mList=RandomInteger[{1,1000},1000] //Sort;
>
> Solve[ Join[mList,mDiff]==Range[1000],mDiff]
>
> Thanks,
> Paul
>
>
> Paul McHale | Electrical Engineer, Energetics Systems | Excelitas
> Technologies Corp.
>
> Phone: +1 937.865.3004 | Fax: +1 937.865.5170 | Mobile: +1
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>
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--
Thanks and Regards,
Priyan Fernando
Mob. +94 772 622 368
