graphs and networks - Truncate TreeForm to show only the top

For some expressions, TreeForm may grow very long. I'm only interested in the top levels of the expression. How can I get the tree form of only the first levels an expression?

For example: how to get the first levels of this expression in tree form?

Nest[1/(1 + #) (1 - #) &, w, 5]

TreeLevel of the above expression

Answer

Can use something like this:

ClearAll[showTopTree];
showTopTree[expr_, level_] :=
  Module[{myHold}, 
     SetAttributes[myHold, HoldAll];
     Function[code,
       TreeForm[Unevaluated@Unevaluated@code],

       HoldAll] @@
    (Hold[#] &@
      DeleteCases[MapAll[myHold, expr], _, {2*level, Infinity}] //.
           myHold[x__] :> x)];

Pretty ugly, but seems to work:

expr = Nest[1/(1 + #) (1 - #) &, w, 5]
Manipulate[showTopTree[expr, n], {n, 1, Depth[expr], 1}]

GraphicsGrid[Partition[showTopTree[expr, #] & /@ Range[6], 3]]

enter image description here

Comments

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