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Re: newbie myHead question

• To: mathgroup at smc.vnet.net
• Subject: [mg47024] Re: [mg47017] newbie myHead question
• From: Oleksandr Pavlyk <pavlyk at phys.psu.edu>
• Date: Mon, 22 Mar 2004 05:18:33 -0500 (EST)
• Organization: Penn State University; Department of Physics
• References: <200403200850.DAA11433@smc.vnet.net>
• Reply-to: pavlyk at phys.psu.edu
• Sender: owner-wri-mathgroup at wolfram.com

Hi Janos,

Since Transpose is undefined on variables with
head "myHead" you could first do transpose and then
apply

Apply[ myHead, Transpose[m] ]

or we can define it:

Unprotect[Transpose];
Transpose[myHead[args__List]] ^:=
    myHead @@ Transpose[{args}];
Protect[Transpose];

Then

Transpose[ myHead[{a,b},{a,b}] ] gives

  myHead[ {a,a}, {b,b} ]

Best,
Sasha

János wrote:

> I have
> 
> m = {{a, b}, {a, b}, {a, b}}
> 
> When I apply Transpose to it, I will have
> 
> Transpose[m]
> 
> {{a, a, a}, {b, b, b}}
> 
> The FullForm of it is
> 
> List[List[a, a, a], List[b, b, b]]
> 
> Now, if I do
> 
> n = Apply[myHead, m]
> 
> I get
> 
> myHead[{a, b}, {a, b}, {a, b}]
> 
> If I apply Transpose to it, I get
> 
> Transpose[n]
> 
> Transpose[myHead[{a, b}, {a, b}, {a, b}]]
> 
> The FullForm of it
> 
> Transpose[myHead[List[a, b], List[a, b], List[a, b]]]
> 
> which is not that I need.  I need
> 
> myHead[{a,a,a},{b,b,b}]
> 
> or
> 
> myHead[List[a, a, a], List[b, b, b]]
> 
> What am I missing ?  What should I do to get myHead[{a,a,a},{b,b,b}] ?
> 
> Thanks ahead,
> 
> János

• References:
  • newbie myHead question
    • From: János <janos.lobb@yale.edu>