Re: ValueQ
- To: mathgroup at smc.vnet.net
- Subject: [mg34343] Re: [mg34327] ValueQ
- From: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>
- Date: Thu, 16 May 2002 05:08:24 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
One Way:
Give up Table,
Use Array.
In[1]:=
a[1]=2;
In[2]:=
Array[ValueQ[a[#]]&,{2}]
Out[2]=
{True,False}
Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/
On Wednesday, May 15, 2002, at 04:35 PM, rainer wrote:
> Hi,
>
> I#m searching for a simple workaround of the following behaviour.
>
> For the symbol 'a' I've defined
>
> In[1]:=
> a[1] = 2;
>
> When I evaluate ValueQ for a defined and for not a defined expression I
> get what I expect:
>
> In[3]:=
> ValueQ[a[1]]
> Out[3]=
> True
>
> In[4]:=
> ValueQ[a[2]]
> Out[4]=
> False
>
> But when I evaluate ValueQ e. g. within a Table I always get True:
>
> In[5]:=
> Table[ValueQ[a[i]], {i, 1, 2}]
> Out[5]=
> {True, True}
>
> The 2nd 'True' is because 'a[i]' is not equal to 'a[2]'. A first
> solution to get the expected result is
>
> In[6]:=
> Table[ToExpression@("ValueQ[a[" <> ToString[i] <> "]]"), {i, 1, 2}]
> Out[6]=
> {True, False}
>
> Does anybody know something better?
>
> Rainer Gruber
> JOHANNES KEPLER UNIVERSITY LINZ
> Institute of Experimental Physics
> Atomic Physics and Surface Science
>
>
>
>