Re: ReplaceAll strange behaviour
- To: mathgroup at smc.vnet.net
- Subject: [mg9373] Re: [mg9312] ReplaceAll strange behaviour
- From: Allan Hayes <hay at haystack.demon.co.uk>
- Date: Sat, 1 Nov 1997 03:33:58 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Gadi Oron <oron at manet.pmmh.espci.fr> [mg9312] ReplaceAll strange
behaviour
> Can anybody enlighten me with the following strange result?
>
> In:= {{1,2},{2,3}} /. {x_ /; Head[x]!=List,y_}:> Circle[{x,y},1]
> Out:=
> {{1,2},{2,3}}
Gadi:
You need Head[x]=!=List in place of Head[x]!=List.
In[1]:= {{1,2},{2,3}} /. {x_ /; Head[x]=!=List,y_}:> Circle[{x,y},1]
Out[1]= {Circle[{1,2},1],Circle[{2,3},1]}
Explanation:
In[2]:= Head[1] !=List
Out[2]= Integer != List
In[3]:= Head[1] =!=List
Out[3]= True
Probably quicker is the following variant:
In[4]:= {{Pi,2},{2,3}} /. {x_?NumericQ,y_}:> Circle[{x,y},1] Out[4]=
{Circle[{Pi,2},1],Circle[{2,3},1]}
Allan Hayes
hay at haystack.demon.co.uk
http://www.haystack.demon.co.uk/
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