Re: Question about Union
- To: mathgroup at smc.vnet.net
- Subject: [mg79231] Re: Question about Union
- From: Bill Rowe <readnewsciv at sbcglobal.net>
- Date: Sat, 21 Jul 2007 04:35:33 -0400 (EDT)
On 7/20/07 at 3:36 AM, yaroslavvb at gmail.com (Yaroslav Bulatov) wrote:
>Union treats 2 numbers as distinct even though SameQ returns true
>for them...how does it test whether values are distinct by default?
>Union[{0.6342350954011774, 0.6342350954011775}]
>0.6342350954011774===0.6342350954011775
The problem here isn't with Union but with SameQ. Per the
documentation, SameQ returns True when the things being compared
are identical. From,
In[6]:= data = {0.6342350954011774, 0.6342350954011775};
In[7]:= SameQ @@ data
Out[7]= True
In[8]:= SameQ @@ (RealDigits /@ data)
Out[8]= False
it is clear SameQ returns true even when two machine precision
numbers are not identical.
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