Re: Testing the Head of List Elements
- To: mathgroup at smc.vnet.net
- Subject: [mg25240] Re: Testing the Head of List Elements
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Sun, 17 Sep 2000 04:47:18 -0400 (EDT)
- References: <8psf4k$9n1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Marshall,
Cases[{"str", 1, -2, 1.2, 1 + 2 I, 2/3, A, aB, AA}, _Complex]
{1 + 2 \[ImaginaryI]}
Try the following in place of _Complex.
_String, _Integer, _Real, _Rational, _Symbol
Also we can use builtin tests, Positive, Negative or NonNegative and those
ending in Q. Please look these up individually on in the Help Browser.
?*Q
ArgumentCountQ MatrixQ
AtomQ MemberQ
DigitQ NameQ
EllipticNomeQ NumberQ
EvenQ NumericQ
ExactNumberQ OddQ
FreeQ OptionQ
HypergeometricPFQ OrderedQ
InexactNumberQ PartitionsQ
IntegerQ PolynomialQ
IntervalMemberQ PrimeQ
InverseEllipticNomeQ SameQ
LegendreQ StringMatchQ
LetterQ StringQ
LinkConnectedQ SyntaxQ
LinkReadyQ TrueQ
ListQ UnsameQ
LowerCaseQ UpperCaseQ
MachineNumberQ ValueQ
MatchLocalNameQ VectorQ
MatchQ
Cases[{"str", "a", 1, -2, Pi, 1.2, 1 + 2 I, 2/3, A, aB, AA}, _?NumericQ]
\!\({1, \(-2\), 1.2`, 1 + 2\ \[ImaginaryI], 2\/3}\)
For characters we can use
Cases[{"str", "a", 1, -2, Pi, 1.2, 1 + 2 I, 2/3, A, aB, AA},
x_String /; StringLength[x] == 1]
{"a"}
--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565
"Marshall Bartlett" <mgb_news at hotmail.com> wrote in message
news:8psf4k$9n1 at smc.vnet.net...
> 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
> --------------------------------------------------------------
>
>
>