Prev: FrontEnd and bash automatization
Next: Easy question, please help to run a function n times
From: Ingolf Dahl on 8 May 2010 07:08
Hi Simon.

Define

backmap[funclist_, x__] := Apply[#1, {x}] & /@ funclist

Then

backmap[{f, g}, x]

gives

{f[x], g[x]}

and

backmap[{Sin[#1] &, Cos[#1] &}, x]

gives

{Sin[x], Cos[x]}

and

backmap[{Sin[#1] &, Cos[#1] &}, Pi/6]

gives

{1/2,Sqrt[3]/2}

You might also do

backmap[{f, g}, x, y]

which gives

{f[x, y], g[x, y]}


Best regards

Ingolf Dahl
Sweden

-----Original Message-----
From: Simon Pearce [mailto:Simon.Pearce(a)nottingham.ac.uk]
Sent: den 7 maj 2010 12:28
Subject: Giving several functions the same argument

Hi Mathgroup,



I have a list of pure functions, which I wish to apply to the same
argument. I can't seem to be able to thread the list of functions over
the argument in a simple way, all the commands like Apply and Map etc
take a single function. I can do it using Table and Part, but it seemed
like there should be a simple command that I'm missing.



For example:



In[1]:= functs = {Sin[#1] &, Cos[#1] &};



In[2]:= functs[x]



Out[2]= {Sin[#1] &, Cos[#1] &}[x]



I want to get the result {Sin[x],Cos[x]} out, without having to use
something of the form:



In[3]:= Table[functs[[i]][x], {i, 1, 2}]



Out[3]= {Sin[x], Cos[x]}



Which seems like it'd be less efficient when I try and use it on long
lists of functions.



Thanks,

Simon


From: Murray Eisenberg on 8 May 2010 07:08
Use Through. E.g.:

Through[{Sin, Cos}[Pi]]
{0, -1}

f = (2 # &); g = (#^2 &);
Through[{f, g}[3]]
{6, 9}

On 5/7/2010 6:28 AM, Simon Pearce wrote:
> Hi Mathgroup,
>
>
>
> I have a list of pure functions, which I wish to apply to the same
> argument. I can't seem to be able to thread the list of functions over
> the argument in a simple way, all the commands like Apply and Map etc
> take a single function. I can do it using Table and Part, but it seemed
> like there should be a simple command that I'm missing.
>
>
>
> For example:
>
>
>
> In[1]:= functs = {Sin[#1]&, Cos[#1]&};
>
>
>
> In[2]:= functs[x]
>
>
>
> Out[2]= {Sin[#1]&, Cos[#1]&}[x]
>
>
>
> I want to get the result {Sin[x],Cos[x]} out, without having to use
> something of the form:
>
>
>
> In[3]:= Table[functs[[i]][x], {i, 1, 2}]
>
>
>
> Out[3]= {Sin[x], Cos[x]}
>
>
>
> Which seems like it'd be less efficient when I try and use it on long
> lists of functions.
>
>
>
> Thanks,
>
> Simon
>

--
Murray Eisenberg murray(a)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

First  |  Prev  | 
Pages: 1 2 3
Prev: FrontEnd and bash automatization
Next: Easy question, please help to run a function n times