Hi Kristina,
Thierry's solution is certainly the "correct" one in terms of keeping
within R's philosophy... but I personally find a series of conditional
assignments easier to understand - see below for an example.
HTH,
Stephan
#####################################################
# Example
freqg <- data.frame(mat=c(1,1,2,2),flank=c(1,2,1,2))
freqg$condition[freqg$mat==1 & freqg$flank==1] <- 1
freqg$condition[freqg$mat==2 & freqg$flank==1] <- 2
freqg
mat flank condition
1 1 1 1
2 1 2 NA
3 2 1 2
4 2 2 NA
#####################################################
ONKELINX, Thierry schrieb:
Dear Kristina,
Use ifelse(). Note that you must use '==' to test for equality. '=' is
an assignment.
Freqg$condition <- with(freqg, ifelse(mat==1 & flank==1, 1, ifelse(mat
== 2 & flank == 1, 2, NA)))
HTH,
Thierry
------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium
Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
thierry.onkel...@inbo.be
www.inbo.be
To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data.
~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey
-----Oorspronkelijk bericht-----
Van: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org] Namens Kristina Schmitz
Verzonden: donderdag 27 mei 2010 11:33
Aan: r-help@r-project.org
Onderwerp: [R] adding column to data frame conditionally
Dear all and thanks in advance for helping me with a rather
stupid question:
I imported a data set ("freqg") into R consisting of 14
variables. Now a want to compute a variable and add it in an
additional column to my data frame. The value of this new
variable ("condition") depends on the values of two other
variables ("mat" and "flank") already included in the data frame.
For example:
if mat=1 and flank=1 -> condition=1
if mat=2 and flank=1 -> condition=2
...
What I got is this code, which doesn't really work (it
results in a new column called "condition" which takes only
the value "TRUE"):
freqg<-transform(freqg,condition=(mat=1)&(flank=1))
Thanks in advance and kind regards!
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