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Re: Re: Setting Negatives to Zero

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82868] Re: [mg82803] Re: [mg82736] Setting Negatives to Zero
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 1 Nov 2007 05:25:32 -0500 (EST)
  • References: <7189487.1193744482274.JavaMail.root@m35> <op.t00vb4u2qu6oor@monster.gateway.2wire.net> <18551847.1193774194904.JavaMail.root@m35> <200710311115.GAA22532@smc.vnet.net>

But Clip could not be possibly be listable (i.e. there is no need to  
check its attributes to know that). Note that a listable function  
does this:

SetAttributes[f, Listable]
f[{a, b}, {c, d}]
{f(a, c), f(b, d)}

So if you try to make Clip Listable you will get in to serious trouble:

SetAttributes[Clip, Listable]

  Clip[{4,5},{2,3}]
Clip::rtwo: The argument 2 at position 2 is expected to be a list of  
a lower clip bound and an upper clip bound. >>
Clip::rtwo: The argument 3 at position 2 is expected to be a list of  
a lower clip bound and an upper clip bound. >>
{Clip(4,2),Clip(5,3)}

On the other hand, you seem to be right that the feature in question  
(which is not Listability) is not documented.

Andrzej Kozlowski


On 31 Oct 2007, at 20:15, DrMajorBob wrote:

> But Clip isn't Listable!
>
> Attributes@Clip
>
> {NumericFunction, Protected}
>
> So how could that work? But it does, evidently:
>
> Clip[Range@100, {5, 95}]
>
> {5, 5, 5, 5, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, \
> 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, \
> 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, \
> 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, \
> 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, \
> 88, 89, 90, 91, 92, 93, 94, 95, 95, 95, 95, 95, 95}
>
> Yet another undocumented feature.
>
> Bobby
>
> On Tue, 30 Oct 2007 14:54:09 -0500, Kevin J. McCann
> <Kevin.McCann at umbc.edu> wrote:
>
>> Thanks, Bobby.
>>
>> Carl Woll gave me the following way to do it.
>>
>> Clip[data,{0,Infinity}]
>>
>> It works and is fast. I had never used Clip before - actually, I  
>> didn't
>> know about it.
>>
>> Kevin
>>
>> DrMajorBob wrote:
>>> data = data /. x_?Negative -> 0
>>>
>>> or something like
>>>
>>> Attributes[negToZero]={Listable}
>>> negToZero[x_?NumericQ] = Sign[x] x
>>> data = negToZero@data
>>>
>>> Bobby
>>>
>>> On Tue, 30 Oct 2007 03:26:37 -0500, Kevin J. McCann
>>> <Kevin.McCann at umbc.edu> wrote:
>>>
>>>> I have a very large data set (64000 x 583) in which negative values
>>>> indicate "no data", unfortunately these negatives are not all  
>>>> the same.
>>>> I would like to efficiently set all these negatives to zero. I know
>>>> that
>>>> I will likely be embarrassed when I see how to do it, but I  
>>>> can't seem
>>>> to remember or figure it out. I should emphasize that because of  
>>>> the
>>>> size of the data set, this needs to be done efficiently. Another
>>>> programming language does it as follows:
>>>>
>>>>         x(x < 0) = 0;
>>>>
>>>> Thanks,
>>>>
>>>> Kevin
>>>
>>>
>>>
>>
>
>
>
> -- 
>
> DrMajorBob at bigfoot.com
>



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