R help - May 2010 - 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!

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.Onkelinx at inbo.be
www.inbo.be

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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

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ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey
  
> -----Oorspronkelijk bericht-----
> Van: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] Namens Kristina Schmitz
> Verzonden: donderdag 27 mei 2010 11:33
> Aan: r-help at 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!
> 
> ______________________________________________
> 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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