Re: Selecting numbers with all odd digits

• To: mathgroup at smc.vnet.net
• Subject: [mg22224] Re: Selecting numbers with all odd digits
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Fri, 18 Feb 2000 02:35:08 -0500 (EST)
• References: <88g51o\$4ee@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Tom:

A slight speed up

Select[Range[6990], Union[OddQ[IntegerDigits[#]]] == {True} &]; // Timing

{3.35 Second, Null}

Select[Range[6990], Select[IntegerDigits[#], EvenQ, 1] === {} &]; // Timing

{2.25 Second, Null}

The 1 in the inner Select terminates the test if an even digit is found

Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Tom De Vries" <tdevries at shop.westworld.ca> wrote in message
news:88g51o\$4ee at smc.vnet.net...
> 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