Re: Transforming a list
- To: mathgroup at smc.vnet.net
- Subject: [mg103155] Re: Transforming a list
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Wed, 9 Sep 2009 04:45:26 -0400 (EDT)
On 9/8/09 at 5:58 AM, donabc at comcast.net (Don) wrote:
>I am given: lst = {{c, e, g}, {d, f}, {e, g}, {f}, {g}, {}}
>I want to form a list of sublists where the first sublist consists
>of the first elements from each sublist of lst, the second sublist
>the second elements from each of the sublists of lst etc.
>The final outcome should be: {{c, d, e, f, g}, {e, f, g}, {g}}
>I can do this by first padding the sublists of lst (to make them the
>same length)and then using Transpose. But how to get rid of the
>trailings 0's?
>For example:
>newLst = Map[PadRight[#, Length[lst[[1]]]] &, lst]
>Transpose[newLst]
>which produces:
>{{c, d, e, f, g, 0}, {e, f, g, 0, 0, 0}, {g, 0, 0, 0, 0, 0}}
>Is there a better way to end up with
>{{c, d, e, f, g}, {e, f, g}, {g}}
One way to do this would be:
In[3]:= list = {{c, e, g}, {d, f}, {e, g}, {f}, {g}, {}};
Table[Cases[list, _?(Length[#] > n - 1 &)][[All, n]], {n,
Max[Length /@ list]}]
Out[4]= {{c,d,e,f,g},{e,f,g},{g}}
Note, you can get the same result by adding one step to the
process you've outlined above. That is:
In[5]:= DeleteCases[#, 0] & /@
Transpose[Map[PadRight[#, Length[list[[1]]]] &, list]]
Out[5]= {{c,d,e,f,g},{e,f,g},{g}}