Re: List of position-specifying functions

• To: mathgroup at smc.vnet.net
• Subject: [mg102365] Re: [mg102351] List of position-specifying functions
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Fri, 7 Aug 2009 05:28:26 -0400 (EDT)
• References: <200908061032.GAA01790@smc.vnet.net>

```Here's the same thing with Map:

plist = {2, 5, 4, 6, 3};
Function[x, #[[x]] &] /@ plist

{#1[[2]] &, #1[[5]] &, #1[[4]] &, #1[[6]] &, #1[[3]] &}

I'm mystified by how you'd use this with SplitBy or GatherBy, though.

Send an example, if you can!

Bobby

On Thu, 06 Aug 2009 05:32:16 -0500, Ray Koopman <koopman at sfu.ca> wrote:

> I have a list of distinct positive integers, such as
>
> In[1]:= plist = {2, 5, 4, 6, 3};
>
> I want to convert it to a list of position-specifying functions,
> such as might be used as the second argument in SplitBy or GatherBy.
> One way that works is:
>
> In[2]:= plist /. p_Integer->(#[[p]]&)
>
> Out[2]= { #1[[2]]&, #1[[5]]&, #1[[4]]&, #1[[6]]&, #1[[3]]& }
>
> I've been trying to get the same thing using Map,
> but I haven't been able to do it. Any suggestions?
>

--
DrMajorBob at bigfoot.com

```

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