Re: Help needed with List!

• To: mathgroup at smc.vnet.net
• Subject: [mg16934] Re: Help needed with List!
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Thu, 8 Apr 1999 02:32:38 -0400
• References: <7ec5kg\$cu2@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```<alvaroo at my-dejanews.com> wrote in message news:7ec5kg\$cu2 at smc.vnet.net...
> Sirs Probably these are FAQs but I am new in this newsgroup and I have not
> been able to solve them. I use Mathematica 3.0:  (i) I need to convert a
long
> integer number in List format. For example if I had the number 123456 I
need
> to convert it into {1,2,3,4,5,6}:  Is it possible with an instruction?
And,
> (ii) I need to delete from a List A the common elements with other List B:
> for example if A = {1,2,3,4} and B = {1,2} I need to delete by an
instruction
> the elements 1, 2 of List B from List A to obtain List C = {3,4}.  I am
> working with integers with 10.000 digits or more so you can appreciate how
> helpful for me it would be to solve these questions.  Thanks in advance.
> alvaroo
>
> -----------== Posted via Deja News, The Discussion Network ==----------
>

Alvaro:
(i)
IntegerDigits[123456 ]
{1,2,3,4,5,6}
and back
FromDigits[%]
123456
But note
IntegerDigits[-123456 ]
{1,2,3,4,5,6}
Sign[-123456]
-1
We can also use
Characters[ToString[-123456]]
{"-","1","2","3","4","5","6"}
and back
StringJoin@@%
"-123456"
ToExpression[%]
-123456

(ii)
A = {1,2,3,4,3, 2} ;B = {1,3} ;
If you will allow ordering and removal of duplicates
Complement[A,B]
{2,4}
if not
DeleteCases[A, Alternatives@@B]
{2,4,2}

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

```

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