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