Problem with access nested list
- To: mathgroup at smc.vnet.net
- Subject: [mg121140] Problem with access nested list
- From: Sam Takoy <sam.takoy at yahoo.com>
- Date: Wed, 31 Aug 2011 06:04:19 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
Hi, Below is a simple code, that constructs the n-dimensional permutation symbol (http://mathworld.wolfram.com/PermutationSymbol.html). I found myself jumping through hoops to accomplish a simple task. The main obstacle was: If I have and n x n x n list "temp", and I want to access the entry temp[[1, 2, 3]], but the numbers 1 2 and 3 are available in a list indicies = {1,2,3}, how do I do it? I tried temp[[list]] but that's not it. What I came up with is essentially Apply[Part[temp, #]&, indices] to convert from a list to arguments. I'm sure I'm missing something. Also, how to avoid the ugly loop? Many thanks in advance! Sam Permutator[n_] := Module[{temp, perms, i}, temp = ConstantArray[0, ConstantArray[n, n]]; setValue[val_][indices__] := Module[{}, Part[temp, indices] = val]; perms = Permutations[Range[1, n]]; For[i = 1, i <= Length[perms], i = i + 1, setValue[Signature[perms[[i]]]] @@ perms[[i]]; ]; temp ];
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