Re: Assigning to a sublist
- To: mathgroup at smc.vnet.net
- Subject: [mg35166] Re: [mg35161] Assigning to a sublist
- From: Andrzej Kozlowski <andrzej at lineone.net>
- Date: Fri, 28 Jun 2002 02:30:51 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Use:
zz[[3,2]] = Append[zz[[3]][[2]], {1, 1, 1, 1, 1}]
instead of
zz[[3]][[2]] = Append[zz[[3]][[2]], {1, 1, 1, 1, 1}]
The latter does not work, because, as the error message tell's you the
in assignments of the form
Part[something,...]= ..., the "something" must be a symbol. The former
assignment above has the FullForm
Part[zz,3,2] so it satisfies this condition while the latter has the
form Part[Part[zz, 3], 2] so it doesn't.
Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/
On Thursday, June 27, 2002, at 01:23 PM, Bob Harris wrote:
> Howdy,
>
> I'm trying to assign a new value to an entry in a sublist (of another
> list),
> and I can't understand why it won't work.
>
> For example, I do the following:
>
> In[1]:= zz = {{2, {{1, 1}}}, {10, {{3, 1}}}, {5, {{2, 1}}}}
> Out[1]= {{2, {{1, 1}}}, {10, {{3, 1}}}, {5, {{2, 1}}}}
>
> In[2]:= zz[[3]][[2]]
> Out[2]= {{2, 1}}
>
> In[3]:= Append[zz[[3]][[2]], {1, 1, 1, 1, 1}]
> Out[3]= {{2, 1}, {1, 1, 1, 1, 1}}
>
> In[4]:= zz[[3]][[2]] = Append[zz[[3]][[2]], {1, 1, 1, 1, 1}]
> Set::"setps : zz[[3]] in assignment of part is not a symbol."
> Out[4]= {{2, 1}, {1, 1, 1, 1, 1}}
>
> For some reason it doesn't like the assignment. What confuses me is
> that is
> zz[[3]][[2]] were just a variable, it would work. Further, if it were
> just
> an entry at the *top* level of a list, it would work, as this example
> shows:
>
> In[5]:= yy = zz[[3]]
> Out[5]= {5, {{2, 1}}}
>
> In[6]:= yy[[2]]
> Out[6]= {{2, 1}}
>
> In[7]:= yy[[2]] = Append[yy[[2]], {1, 1, 1, 1, 1}]
> Out[7]= {{2, 1}, {1, 1, 1, 1, 1}}
>
> So it seems like the issue is just that deeply nested things don't
> behave
> like things that are not as deeply nested. Am I right about that? How
> can
> I modify an entry in a sublist?
>
> Thanks,
> Bob H
>
>
>
>