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Re: Combining elements of a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg108850] Re: Combining elements of a list
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sun, 4 Apr 2010 07:44:11 -0400 (EDT)

I'm going to assume you don't really have symbols (t, h, etc.) but 
rather one-letter strings ("t", "h", etc.) here.

The basic function you want is StringJoin.  Thus:

   StringJoin[{"t", "h", "i", "s"}]
this

Next, you have your list of lists:

  lis = {{"t", "h", "i", "s"}, {"i", "s"}, {"a"}, {"t", "e", "s", "t"}};

(I left out the last word.)  So Map the function StringJoin onto that at 
level 1:

   Map[StringJoin, lis, 1]
{"this", "is", "a", "test"}

Now you need to append a blank to each word (except the last).  For a 
single string str StringInsert[str," ",-1] does it, as in:

   trial=StringInsert["this"," ",-1]
this
   (* you can't see the trailing blank here, so... *)
   StringLength[trial]
5

(You could also use StringJoin instead of StringInsert.)

Now Map that function of appending a blank onto the list of words:

   appended = Map[StringInsert[#, " ", -1] &, words]
{this ,is ,a ,test }

Same thing, abbreviated:

   StringInsert[#, " ", -1] & /@ words

Finally, join all the individual (blank-trailed) words into a single 
string and delete the final trailing blank:

   StringTrim@StringJoin[appended]

Obviously, all those steps could be combined, encapsulated into a single 
function:

   sentenceFromLetters[lis_] :=
      StringTrim@
      StringJoin[StringInsert[#, " ", -1] & /@ Map[StringJoin, lis, 1]]

Doubtless there are terser, or at least alternative ways, to do this 
using pattern-matching for at least some of the steps.


If your original list really consisted of lists of symbols rather than 
lists of one-character strings, you could first convert that to a list 
of lists of one-character strings by using ToString.



On 4/3/2010 7:09 AM, ebaugh at illinois.edu wrote:
> How could I go from:
> {h,e,l,l,o}
> to
> {hello}?
>
> That is the first step of what I am really looking to do. Which is
> to go from:
> {{t,h,i,s},{i,s},{a},{t,e,s,t},{m,e,s,s,a,g,e}}
> to
> "this is a test message"
>
> Thanks all,
> Jason Ebaugh
>
>
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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