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Re: Map, List

  • To: mathgroup at
  • Subject: [mg55103] Re: [mg55066] Map, List
  • From: DrBob <drbob at>
  • Date: Sat, 12 Mar 2005 02:36:53 -0500 (EST)
  • References: <>
  • Reply-to: drbob at
  • Sender: owner-wri-mathgroup at

>> What general principle applies that makes all such things functions?

Two principles:

1) Just about anything can be used as a function. 1[2] is valid syntax, for instance.
2) Nothing is strictly a function.

f[x] isn't a function f applied to an argument x; it's an expression which, if it matches a stored pattern for f, is replaced by a new expression. The new expression may do many things, aside from returning a value. Side-effects can keep f from mimicking a function at all, in the usual sense.

Mathematica's pattern-matching paradigm is far richer and more varied than a simple function-argument situation.


On Fri, 11 Mar 2005 04:20:42 -0500 (EST), Steve Gray <stevebg at> wrote:

> 	I wanted to convert
> {a,b,c} to
> {{a},{b},{c}}, (just an example)
> and it occured to me that since List[xx] = {xx}, I could do
> ml=Map[List,{a,b,c}] and get
> ml={{a},{b},{c}},
> making List in this case the inverse of Flatten. Now,assuming a,b,c have appropriate integer values,
> I can do
> Delete[ggon, ml]
> where ggon is a list from which I want to delete an arbitrary set of list members.
> Of course this worked. My only problem is that I might  not have thought of this obvious (in
> retrospect) operation. Using List as a function is not mentioned in any of my several books. What
> general principle applies that makes all such things functions?
> Thank you.
> Steve Gray

DrBob at

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      • From: Steve Gray <>
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