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MathGroup Archive 1998

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RE: variation on Split

  • To: mathgroup at smc.vnet.net
  • Subject: [mg12684] RE: [mg12636] variation on Split
  • From: Ersek_Ted%PAX1A at mr.nawcad.navy.mil
  • Date: Mon, 1 Jun 1998 23:16:55 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

lucb"@ea.com   wrote:

|
|Split[{a,b,c,d,d,e,f,g,g,h,h,h}] returns
|{{a},{b},{c},{d,d},{e},{f},{g,g},{h,h,h}} |
|What do you have to do to get:
|{{a,b,c},{d,d},{e,f},{g,g},{h,h,h}} |?
|

Here is the way I would do it.
__________________________________

In[1]:=
lst=Split[{a,b,c,d,d,e,f,g,g,h,h,h}]

Out[1]=
{{a},{b},{c},{d,d},{e},{f},{g,g},{h,h,h}}


The next line splits the list into adjacent lists that have only one
element  and other lists that have more than one element.

In[2]:=
ss=Split[lst,(Length[#1]===Length[#2]===1)&]

Out[2]=
{{{a},{b},{c}},{{d,d}},{{e},{f}},{{g,g}},{{h,h,h}}}


Now I apply the function Join to each sublist above.

In[3]:=
Apply[Join,ss,1]

Out[3]=
{{a,b,c},{d,d},{e,f},{g,g},{h,h,h}}

________________________________
The next line is a new function that puts all the above in a module.

In[4]:=
Split2[lst_List]:=Module[{ss},
      ss=Split[ Split[lst], (Length[#1]===Length[#2]===1)&];
      Apply[Join, ss, 1]
   ]


In[5]:=
Split2[{a,b,c,d,d,e,f,g,g,h,h,h}]

Out[5]=
{{a,b,c},{d,d},{e,f},{g,g},{h,h,h}}


________________________________________ Members of the group can
explain further if you don't understand "
(Length[#1]===Length[#2]===1)& ".


Ted Ersek



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