[R] Replacing elements of a list over a certain threshold

[Joris Meys]

You shouldn't use sapply/lapply for this but use the indices

> set.seed(1)
> r <- round(runif(100000,1,10))
> treshold <- 5
> head(r)
[1] 3 4 6 9 3 9

> system.time( r[ r>threshold ] <- threshold )
   user  system elapsed
      0       0       0

> head(r)
[1] 3 4 5 5 3 5



On Mon, Jun 21, 2010 at 2:03 PM, Christos Argyropoulos
<argchris at hotmail.com> wrote:
>
> 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 at ipec.co.uk
>> To: r-help at 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 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.
>
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> ______________________________________________
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>



-- 
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
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