Re: a[[2]][[3]] = 1 error? why?

• To: mathgroup at smc.vnet.net
• Subject: [mg8899] Re: a[[2]][[3]] = 1 error? why?
• From: Paul Abbott <paul at physics.uwa.edu.au>
• Date: Thu, 2 Oct 1997 22:56:52 -0400
• Organization: University of Western Australia
• Sender: owner-wri-mathgroup at wolfram.com

```charles loboz wrote:

> a=Table[i*j,{i,1,3},{j,1,3}];
> a[[2]][[3]]
>
> answer : 6 (as it should be)
> so why assignment to
> a[[2]][[3]] = 3
> doesn't work?

In[1]:= a = Table[i*j, {i, 1, 3}, {j, 1, 3}];

In[2]:= a[[2]][[3]]
Out[2]= 6

Entering

In[3]:= a[[2]][[3]] = 3

results in

Set::"setps": a[[2]] in assignment of part is not a symbol."

Out[3]= 3

which tells you that you cannot use this syntax (i.e. you cannot use Set
or =) because a[[2]] is not a symbol.  However, you can do what you want
using the alternative syntax

In[4]:= a[[2,3]] = 3
Out[4]= 3

In[5]:= a
Out[5]= {{1, 2, 3}, {2, 4, 3}, {3, 6, 9}}

Cheers,
Paul

____________________________________________________________________
Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia
Nedlands WA  6907                     mailto:paul at physics.uwa.edu.au
AUSTRALIA                             http://www.pd.uwa.edu.au/~paul

God IS a weakly left-handed dice player
____________________________________________________________________

```

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