Re: Appending an element to a list
- To: mathgroup at smc.vnet.net
- Subject: [mg23910] Re: Appending an element to a list
- From: Hartmut Wolf <hwolf at debis.com>
- Date: Fri, 16 Jun 2000 00:56:51 -0400 (EDT)
- Organization: debis Systemhaus
- References: <8i9nta$27l@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Felix Farkas schrieb: > > i do have a problem, which is probably very easy, but i couldn't find > a reasonable way to solve it. I would appreciate very much any hint. > > I have a list of lists. My purpose is to append a new elements to this > list. These elements are generated by some function. Sometimes the > output of the function is an empty list meaning no element. In this > situation Append includes the new element in the list. i would like to > avoid this behaviour. > > ex: > > In[1]:= d={} > Out[1]= {} > > In[2]:= Append[{{2,2},{3,3}},d] > Out[2]:= {{2,2},{3,3},{}} > Perhaps this might be useful: In[1]:= appendnoemptylistTo[expr_, {}] := expr In[2]:= appendnoemptylistTo[expr_, elem_] := AppendTo[expr, elem] In[3]:= b = d = e = {}; In[7]:= collector = {}; In[8]:= Scan[appendnoemptylistTo[Unevaluated[collector], #] &, {a, b, c, d, e, f}] In[9]:= collector Out[9]= {a, c, f} Kind regards, Hartmut Wolf