list referencing with [[ ]][[ ]]

• To: mathgroup at smc.vnet.net
• Subject: [mg13969] list referencing with [[ ]][[ ]]
• From: tdelling at ews.uiuc.edu (Tim Dellinger)
• Date: Fri, 11 Sep 1998 15:06:57 -0400
• Organization: University of Illinois at Urbana-Champaign
• Sender: owner-wri-mathgroup at wolfram.com

```According to "the book" section 1.8.4,

t[[1]][[2]] "is equivalent to" t[[1,2]], "but is clumsier to write"

and that is all that I can find concerning the difference between the
two ways of refering to a list element.

But...

In[37]:=
alist = {{1,2},{3,4}}; alist[[2,1]] = 7 ; alist

Out[37]=
{{1,2},{7,4}}

So far so good, and yet...

In[39]:=
anotherlist = {{1,2},{3,4}}; anotherlist[[2]][[1]] = 7
Set::"setps":
"\!\(anotherlist \\[LeftDoubleBracket] 2 \\[RightDoubleBracket]\) in
\
assignment of part is not a symbol."
Out[39]=
7

What's the problem here?  Is there a difference between the two ways of
referencing list elements that "the book" neglects to mention?

--
--
"Perhaps my most deeply rooted hobby is to understand         Tim
Dellinger
the mechanisms of simple and familiar
tdelling at uiuc.edu
natural phenomena." Irving Langmuir
http://www.ews.uiuc.edu/~tdelling

```

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