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Kurt_Helf at nps.gov

2010-Sep-21 19:47 UTC

[R] R-help Digest, Vol 91, Issue 21

All
     Is there a script in R equivalent to the "if then" transforms one
can
perform in Systat?  For example, I want to create a "Treatment" column
coded either 1 or 2 for twelve field sites in a large data set.  Ideally,
I'd be able to tell R to code sites a-f as 1 and sites g-l as 2.
Cheers
Kurt

***************************************************************
Kurt Lewis Helf, Ph.D.
Ecologist
EEO Counselor
National Park Service
Cumberland Piedmont Network
P.O. Box 8
Mammoth Cave, KY 42259
Ph: 270-758-2163
Lab: 270-758-2151
Fax: 270-758-2609
****************************************************************
Science, in constantly seeking real explanations, reveals the true majesty
of our world in all its complexity.
-Richard Dawkins

The scientific tradition is distinguished from the pre-scientific tradition
in having two layers.  Like the latter it passes on its theories but it
also passes on a critical attitude towards them.  The theories are passed
on not as dogmas but rather with the challenge to discuss them and improve
upon them.
-Karl Popper

...consider yourself a guest in the home of other creatures as significant
as yourself.
-Wayside at Wilderness Threshold in McKittrick Canyon, Guadalupe Mountains
National Park, TX

Cumberland Piedmont Network (CUPN) Homepage:
http://tiny.cc/e7cdx

CUPN Forest Pest Monitoring Website:
http://bit.ly/9rhUZQ

CUPN Cave Cricket Monitoring Website:
http://tiny.cc/ntcql

CUPN Cave Aquatic Biota Monitoring Website:
http://tiny.cc/n2z1o

Marc Schwartz

2010-Sep-21 20:01 UTC

head link

[R] R-help Digest, Vol 91, Issue 21

On Sep 21, 2010, at 2:47 PM, Kurt_Helf at nps.gov wrote:
> All
>     Is there a script in R equivalent to the "if then" transforms
one can
> perform in Systat?  For example, I want to create a "Treatment"
column
> coded either 1 or 2 for twelve field sites in a large data set.  Ideally,
> I'd be able to tell R to code sites a-f as 1 and sites g-l as 2.
> Cheers
> Kurt

Something along the lines of:

  Treatment <- ifelse(sites %in% c("a", "b",
"c", "d", "e", "f"), 1, 2)

should work.  See ?"%in%" and ?ifelse

HTH,

Marc Schwartz

Peter Dalgaard

2010-Sep-21 20:17 UTC

head link

[R] R-help Digest, Vol 91, Issue 21

On 09/21/2010 09:47 PM, Kurt_Helf at nps.gov wrote:> All
>      Is there a script in R equivalent to the "if then"
transforms one can
> perform in Systat?  For example, I want to create a "Treatment"
column
> coded either 1 or 2 for twelve field sites in a large data set.  Ideally,
> I'd be able to tell R to code sites a-f as 1 and sites g-l as 2.
> Cheers
> Kurt
Well, er, sort of.

Actually, there are multiple techniques in R to achieve the same effects
as you'd get using if statements in other languages.

e.g.

f.new <- f
levels(f.new) <- rep(1:2, each=6)

or

f.new <-f
levels(f.new) <- list("1"=letters[1:6],"2"=letters[7:12])

or

f.new <- factor(rep(1:2, each=6))[f]

or

f.new <- (as.numeric(f) > 6) + 1

or

f.new <- factor(ifelse(as.numeric(f) <= 6), 1, 2))

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

David Winsemius

2010-Sep-21 20:35 UTC

head link

[R] R-help Digest, Vol 91, Issue 21

On Sep 21, 2010, at 3:47 PM, Kurt_Helf at nps.gov wrote:
> All
>     Is there a script in R equivalent to the "if then" transforms
> one can
> perform in Systat?  For example, I want to create a "Treatment"
column
> coded either 1 or 2 for twelve field sites in a large data set.   
> Ideally,
> I'd be able to tell R to code sites a-f as 1 and sites g-l as 2.
?ifelse  # probably the way most normally adjusted people would do it.

?match

 > selection <- letters[1:15][sample( 1:15, 30, replace=TRUE)]
 > selection
  [1] "e" "k" "l" "b" "d"
"e" "b" "b" "o" "o"
"c" "n" "i" "f" "g"
"k"
"b" "f" "k"
[20] "e" "m" "d" "h" "e"
"c" "o" "e" "h" "a"
"i"

 > match(selection, letters[1:7])   # over shot "f", guess I cannot
count.
  [1]  5 NA NA  2  4  5  2  2 NA NA  3 NA NA  6  7 NA  2  6 NA  5 NA   
4 NA  5  3
[26] NA  5 NA  1 NA
 >  # can be used for logical indexing
  [1]  TRUE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE   
TRUE FALSE
[13] FALSE  TRUE  TRUE FALSE  TRUE  TRUE FALSE  TRUE FALSE  TRUE  
FALSE  TRUE
[25]  TRUE FALSE  TRUE FALSE  TRUE FALSE
 > !is.na(match(selection, letters[8:15]) )
  [1] FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE  
FALSE  TRUE
[13]  TRUE FALSE FALSE  TRUE FALSE FALSE  TRUE FALSE  TRUE FALSE  TRUE  
FALSE
[25] FALSE  TRUE FALSE  TRUE FALSE  TRUE
 > # testing to see if any fell through the cracks
 > !is.na(match(selection, letters[8:15]) )| !is.na(match(selection,  
letters[1:7]) )
  [1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE  
TRUE TRUE
[16] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE  
TRUE TRUE

Could do this for the case you requested:
Treatment <- 2 - !is.na(match(selection, letters[1:7]) )

TRUE is 1 and FALSE is zero in Boolean arithmetic (which R supports).

-- 
David.
> Cheers
> Kurt
>
> ***************************************************************
> Kurt Lewis Helf, Ph.D.
> Ecologist
> EEO Counselor
> National Park Service
> Cumberland Piedmont Network
> P.O. Box 8
> Mammoth Cave, KY 42259
> Ph: 270-758-2163
> Lab: 270-758-2151
> Fax: 270-758-2609
> ****************************************************************
> Science, in constantly seeking real explanations, reveals the true  
> majesty
> of our world in all its complexity.
> -Richard Dawkins
>
> The scientific tradition is distinguished from the pre-scientific  
> tradition
> in having two layers.  Like the latter it passes on its theories but  
> it
> also passes on a critical attitude towards them.  The theories are  
> passed
> on not as dogmas but rather with the challenge to discuss them and  
> improve
> upon them.
> -Karl Popper
>
> ...consider yourself a guest in the home of other creatures as  
> significant
> as yourself.
> -Wayside at Wilderness Threshold in McKittrick Canyon, Guadalupe  
> Mountains
> National Park, TX
>
> Cumberland Piedmont Network (CUPN) Homepage:
> http://tiny.cc/e7cdx
>
> CUPN Forest Pest Monitoring Website:
> http://bit.ly/9rhUZQ
>
> CUPN Cave Cricket Monitoring Website:
> http://tiny.cc/ntcql
>
> CUPN Cave Aquatic Biota Monitoring Website:
> http://tiny.cc/n2z1o
>
> ______________________________________________
> 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.
David Winsemius, MD
West Hartford, CT

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