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MathGroup Archive 2000

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Re: Testing the Head of List Elements

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25264] Re: Testing the Head of List Elements
  • From: Harold Skolnick <hskolnic at ix.netcom.com>
  • Date: Sun, 17 Sep 2000 04:47:54 -0400 (EDT)
  • References: <8psf4k$9n1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi ,

(*List*)

In[25]:=
ll = {aa, 2.333, {{1.599999, 2}, 2.333333, "3"}, {"word", {w, 0}}}
Out[25]=
{aa, 2.333, {{1.6, 2}, 2.33333, "3"}, {"word", {w, 0}}}

(*Heads of elements*)
In[26]:=
Map[Head, ll, {-1} ]
Out[26]=
{Symbol, Real, {{Real, Integer}, Real, String}, {String, {Symbol, Integer}}}

(*Selected elements with head string*)

In[27]:=qq = Cases[ll, _String, {-1} ]
Out[27]={"3", "word"}

Hope this helps.
harold

Marshall Bartlett wrote:

> I'm something of a newbie with Mathematica; please excuse my ignorance.
>
> I am looking for a clever way to select elements from a list based on their
> type (Head).  Specifically, I want to extract all the elements of type
> dtring from a list of elements of different types (string, number,
> character, etc.).
>
> Any suggestions?
>
> --
> --------------------------------------------------------------
> Marshall Bartlett
> Department of Geology and Geophysics
> University of Utah
> mgb_news at hotmail.com
> --------------------------------------------------------------



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