R help - Jun 2010 - Replacing elements of a list over a certain threshold

Dear List,

I have a list of length ~1000 filled with numerics. I need to replace 
the elements of this list that are above a certain numerical threshold 
with the value of the threshold.

e.g
example=list(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
threshold=5
<magic code goes here>
example=(1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 4, 3, 2, 1).

I have written a crude script that achieves this but it's very slow. Is 
there a way to do this using some R function?

Crude script: http://pastebin.com/3KSfi8nD

"magic" code:
example[example>threshold] <-threshold

Cheers
Joris

On Mon, Jun 21, 2010 at 12:34 PM, Jim Hargreaves <james at ipec.co.uk>
wrote:
> Dear List,
>
> I have a list of length ~1000 filled with numerics. I need to replace the
> elements of this list that are above a certain numerical threshold with the
> value of the threshold.
>
> e.g
> example=list(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
> threshold=5
> <magic code goes here>
> example=(1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 4, 3, 2, 1).
>
> I have written a crude script that achieves this but it's very slow. Is
> there a way to do this using some R function?
>
> Crude script: http://pastebin.com/3KSfi8nD
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Applied mathematics, biometrics and process control

tel : +32 9 264 59 87
Joris.Meys at Ugent.be
-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php

Hi, 
You should use the sapply/lapply for such operations.
> r<-round(runif(100000,1,10))
> head(r)
[1] 3 7 6 3 2 8
> filt<-function(x,thres) ifelse(x<thres,x,thres)
> system.time(r2<-sapply(r,filt,thres=5))
   user  system elapsed 
   3.36    0.00    3.66 
> head(r2)
[1] 3 5 5 3 2 5


To return a list, replace "sapply" with "lapply"

Christos


> Date: Mon, 21 Jun 2010 11:34:01 +0100
> From: james@ipec.co.uk
> To: r-help@r-project.org
> Subject: [R]  Replacing elements of a list over a certain threshold
> 
> Dear List,
> 
> I have a list of length ~1000 filled with numerics. I need to replace 
> the elements of this list that are above a certain numerical threshold 
> with the value of the threshold.
> 
> e.g
> example=list(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
> threshold=5
> <magic code goes here>
> example=(1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 4, 3, 2, 1).
> 
> I have written a crude script that achieves this but it's very slow. Is
> there a way to do this using some R function?
> 
> Crude script: http://pastebin.com/3KSfi8nD
> 
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
 		 	   		  
_________________________________________________________________
Hotmail: Free, trusted and rich email service.

	[[alternative HTML version deleted]]

Try this also:

replace(example, example > threshold, threshold)

On Mon, Jun 21, 2010 at 7:34 AM, Jim Hargreaves <james@ipec.co.uk> wrote:
> Dear List,
>
> I have a list of length ~1000 filled with numerics. I need to replace the
> elements of this list that are above a certain numerical threshold with the
> value of the threshold.
>
> e.g
> example=list(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
> threshold=5
> <magic code goes here>
> example=(1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 4, 3, 2, 1).
>
> I have written a crude script that achieves this but it's very slow. Is
> there a way to do this using some R function?
>
> Crude script: http://pastebin.com/3KSfi8nD
>
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

Jim Hargreaves <james at ipec.co.uk> [Mon, Jun 21, 2010 at 12:34:01PM
CEST]:
> Dear List,
> 
> I have a list of length ~1000 filled with numerics. I need to
> replace the elements of this list that are above a certain numerical
> threshold with the value of the threshold.
> 
> e.g
> example=list(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
> threshold=5
> <magic code goes here>
> example=(1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 4, 3, 2, 1).
> 
lapply(example, min, 5)

-- 
Johannes H?sing               There is something fascinating about science. 
                              One gets such wholesale returns of conjecture 
mailto:johannes at huesing.name  from such a trifling investment of fact.
http://derwisch.wikidot.com         (Mark Twain, "Life on the
Mississippi")

On Jun 22, 2010, at 2:14 PM, Johannes Huesing wrote:
> Jim Hargreaves <james at ipec.co.uk> [Mon, Jun 21, 2010 at 12:34:01PM
> CEST]:
>> Dear List,
>>
>> I have a list of length ~1000 filled with numerics. I need to
>> replace the elements of this list that are above a certain numerical
>> threshold with the value of the threshold.
>>
>> e.g
>> example=list(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2,  
>> 1)
>> threshold=5
>> <magic code goes here>
>> example=(1, 2, 3, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 4, 3, 2, 1).
>>
>
> lapply(example, min, 5)
Perhaps wrapped in unlist( ) if a vector is desired.

The same strategy would work with pmin and probably be faster (albeit  
not a big deal if the list is only 1000 elements long:

unlist( pmin(example, 5) )

>
> -- 
> Johannes H?sing

David Winsemius, MD
West Hartford, CT