On Sep 21, 2010, at 3:47 PM, kurt_h...@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
****************************************************************
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