RE: Assigning to a sublist
- To: mathgroup at smc.vnet.net
- Subject: [mg35170] RE: [mg35161] Assigning to a sublist
- From: "DrBob" <majort at cox-internet.com>
- Date: Fri, 28 Jun 2002 02:30:57 -0400 (EDT)
- Reply-to: <drbob at bigfoot.com>
- Sender: owner-wri-mathgroup at wolfram.com
You can Set a Part of a variable, as in
yy[[2]]=(anything)
However, when you try
zz[[3]][[2]] = (anything)
you are trying to Set a Part of zz[[3]] (which is a constant), not Part
of zz, as you intend.
The solution is to Set a Part of zz, as follows:
zz = {{2, {{1, 1}}}, {10, {{3, 1}}}, {5, {{2, 1}}}};
zz[[3, 2]] = Append[zz[[3]][[2]], {1, 1, 1, 1, 1}];
zz
{{2, {{1, 1}}}, {10, {{3, 1}}}, {5, {{2, 1}, {1, 1, 1, 1, 1}}}}
or equivalently:
zz = {{2, {{1, 1}}}, {10, {{3, 1}}}, {5, {{2, 1}}}};
AppendTo[zz[[3, 2]], {1, 1, 1, 1, 1}];
zz
{{2, {{1, 1}}}, {10, {{3, 1}}}, {5, {{2, 1}, {1, 1, 1, 1, 1}}}}
Look up Part in the Help browser, for more ideas.
Bobby Treat
-----Original Message-----
From: Bob Harris [mailto:nitlion at mindspring.com]
To: mathgroup at smc.vnet.net
Subject: [mg35170] [mg35161] Assigning to a sublist
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