Re: Selecting numbers with all odd digits
- To: mathgroup at smc.vnet.net
- Subject: [mg22253] Re: [mg22170] Selecting numbers with all odd digits
- From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
- Date: Sat, 19 Feb 2000 01:33:57 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
I noticed that in a fit of blindeness I put a spurious ==True into a
predicate. The correct code is of course:
Select[ Range[699], And @@ OddQ[IntegerDigits[#]]&]
--
on 2/17/00 4:30 PM, Andrzej Kozlowski at andrzej at platon.c.u-tokyo.ac.jp
wrote:
> on 00.2.17 3:23 PM, Tom De Vries at tdevries at shop.westworld.ca wrote:
>
>> Hello all,
>>
>> In one of the math classes I am teaching we are doing some work with
>> permutations and combinations. One question in the text was, "how many
>> positive integers less than 700 have all odd digits?"
>>
>> I had done the question "by hand" and then wondered how to use Mathematica
>> to demonstrate that the solution was the correct one.
>>
>> I am still very far down on the learning curve in most things, but I managed
>> to bludgeon my way to an answer (thankfully the same as mine!)
>>
>> Select[
>>
>> Range[699],
>>
>> Union[ OddQ [ IntegerDigits[#]]] == {True} &
>>
>> ]
>>
>> I am sure my trial and error method can be improved upon. I am not talking
>> speed as much as simply using Mathematica in a way that makes sense and
>> would be more logical??
>>
>> Thanks for any suggestions might have!
>>
>> Tom De Vries
>> Edmonton, Alberta
>> Canada
>>
>>
>
> Your code is basically fine. The following seems to me just a little bit
> more natural and also somewhat faster:
>
>
> In[5]:=
> Select[ Range[10^5], And @@ OddQ [ IntegerDigits[#]] == True & ]; // Timing
> Out[5]=
> {13.7167 Second, Null}
> In[6]:=
> Select[Range[10^5], Union[ OddQ [ IntegerDigits[#]]] == {True} & ]; //
> Timing
> Out[6]=
> {23.7 Second, Null}
>
> --
> Andrzej Kozlowski
> Toyama International University
> Toyama, Japan
> http://sigma.tuins.ac.jp/
>
>
Andrzej Kozlowski
Toyama International University
JAPAN
http://sigma.tuins.ac.jp