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MathGroup Archive 2006

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Re: ReplaceAll applied to List

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72325] Re: ReplaceAll applied to List
  • From: "dimitris" <dimmechan at yahoo.com>
  • Date: Tue, 26 Dec 2006 05:58:37 -0500 (EST)
  • References: <em8jdu$pel$1@smc.vnet.net>

Everything is normal. Look at the following example

In[18]:=
{2.3, 4, {7/8}, a, b, I, {{I^2}}} /. x_ /; NumberQ[x] -> x^2

Out[18]=
{5.289999999999999, 16, {49/64}, a, b, -1, {{1}}}

The rule is applied to all the levels of the expression. But

In[19]:=
Cases[{2.3, 4, {7/8}, a, b, I, {{I^2}}}, x_ /; NumberQ[x] -> x^2]

Out[19]=
{5.289999999999999, 16, -1}

Only at level one here.

Regards
Dimitris



Hannes Kessler wrote:
> Hello,
>
> I want to apply transformation rules to those elements of a list which
> are not lists themselves. The structure of the list is unknown in
> advance.
>
> The following simple examples illustrate my my problems with ReplaceAll
> and List:
>
> Expected result:
> {1., {2}, 3} /. x_?NumericQ :> g
> --> {g,{g},g}
>
> Unexpected result - inspite of AtomQ[{1., {2}, 3}] giving False
> {1., {2}, 3} /. x_?AtomQ :> g
> --> g[g, g[g], g]
>
> Similarly unexpected result - inspite of Not[ListQ[{1., {2}, 3}]]
> giving False
> {1., {2}, 3} /. x_?(Not[ListQ[#]] &) :> g
> --> g[g, g[g], g]
>
> Any explanations for this behavior?
> 
> Thanks in advance,
> Hannes Kessler


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