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Re: Transform list of numbers into pure functions using replace rule

  • To: mathgroup at smc.vnet.net
  • Subject: [mg89479] Re: Transform list of numbers into pure functions using replace rule
  • From: dh <dh at metrohm.ch>
  • Date: Tue, 10 Jun 2008 07:13:17 -0400 (EDT)
  • References: <g2lb8t$964$1@smc.vnet.net>


Hi Mac,

you have a mistake in the pattern, it should read: x_/;NumberQ[x] or 

x?NumberQ. Then there is no need to convert to a string:

{1,2,f[x]}/.x_?NumberQ->Function[x]

or

{1,2,f[x]}/.x_?NumberQ->(x&)

hope this helps, Daniel





Mac wrote:

> Hello,

> 

> I'm developed a program to invert satellite observations into

> geophysical variables such as forest biomass. One of the input

> parameters are the errors in the observation channels which can be

> either constant or a function. To be consistent the program expects

> all errors to be functions but they can also be constant functions

> e.g. if the error is 4 then the input parameter is "4&".

> 

> I've however hit a problem with the replacement rule that allows me to

> transform all input errors into a function. The following works as

> expected in that constants in the list are transformed into virtual

> functions and functions in the list are left alone.

> 

> In[40]:= If[NumberQ[#], ToExpression[ToString[#] <> "&"], #] & /@ {1,

>   2, 3 &, f[x]}

> 

> Out[40]= {1 &, 2 &, 3 &, f[x]}

> 

> However, I cannot find a replacement rule to do the same job. Here is

> one try:

> 

> In[39]:= {1, 2, f[x]} /. x_ /; NumberQ -> Hold[x &]

> 

> Out[39]= {1, 2, f[x]}

> 

> Any help would be appreciated.

> 

> Mac

> 

> 





-- 



Daniel Huber

Metrohm Ltd.

Oberdorfstr. 68

CH-9100 Herisau

Tel. +41 71 353 8585, Fax +41 71 353 8907

E-Mail:<mailto:dh at metrohm.com>

Internet:<http://www.metrohm.com>




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