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Re: Building List


Bruce W. Colletti wrote:
> Re Mathematica 5.0.1.0.
> I have a list of lists -- e.g., L = { {1,2},{3,4,5,6},{7,8} } -- and 
> want to replace element-lists (whose length exceeds 2) with another list 
> built from that element.  All else is untouched.
> For instance, using L above, replace {3,4,5,6} with {3,4}, {3,5}, {3,6}. 
>  This transforms L to the desired form { {1,2}, {3,4}, {3,5}, {3,6}, 
> {7,8} }.
> Although I can do this using Sow and Reap, am hoping there's an easier 
> way using rules (/.).  In general, I want to replace those L-elements x 
> (that meet a criterion) with foo[x]. 
> Thanks.
> Bruce

In[1]:= myRule=
{a___, b_List /; Length[b] > 2, c___} :> 
{a, Sequence @@ Thread[{First[b],Rest[b]}],c};

In[2]:= { {1,2},{3,4,5,6},{7,8} } /. myRule
Out[2]={{1,2},{3,4},{3,5},{3,6},{7,8}}

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