Hi Peter!

The 'if' function operate on a single logical expression, while you provided
a vector. What your code does at present is subtract 5 from all values in
rr.dia.2m if the first value in med.hyper is 1 and otherwise simply returns
all values as is. Since you have no reproducible data, it's harder to
provide a fix, but you may want to check ?for or (preferably) ?apply. Or
simply try :

rr.dia.2m.corr<-rr.dia.2m
rr.dia.2m.corr[med.hyper==1]<-rr.dia.2m.corr[med.hyper==1]-5
#NOTE: untested

hth/ Rafael

2010/6/8 Peter Lercher <Peter.Lercher@i-med.ac.at>

> Dear colleagues,
>
> What did I not understand ?
>
> ->my intention
> I want to create a new variable:
> In plain language:
> If someone is taking anithypertensive treatment (med.hyper==1)
> table(med.hyper)
> med.hyper
>  0   1
> 472  97
> I want to subtract 5 mmHg (rr.dia.2m-5) from the measured diastolic blood
> pressure (rr.dia.2m)
> if not treated - the value of the measured diastolic blood pressure should
> remain the same
>
> ->my code (data frame is attached !)
> rr.dia2.corr<-if(med.hyper==1)
> {
> rr.dia.2m-5
> } else
> {
> rr.dia2.corr==rr.dia.2m
> }
>
> R warning
> Warnmeldung:
> In if (med.hyper == 1) { :
>  Bedingung hat Länge > 1 und nur das erste Element wird benutzt
> "Only first condition is use"
> which you can see from the result (simply 5 mm was subtracted and the
> second condition was taken into account)
>
> > describe(rr.dia.2m)
> rr.dia.2m
>     n missing  unique    Mean     .05     .10     .25     .50     .75
> .90     .95
>   546      26     110   85.32   67.00   71.50   77.62   84.50   92.00
> 99.25  105.00
>
> lowest :  45.0  57.0  60.0  61.0  62.0, highest: 127.5 128.5 129.5 142.5
> 146.5
> > describe(rr.dia2.corr)
> rr.dia2.corr
>     n missing  unique    Mean     .05     .10     .25     .50     .75
> .90     .95
>   546      26     110   80.32   62.00   66.50   72.62   79.50   87.00
> 94.25  100.00
>
> lowest :  40.0  52.0  55.0  56.0  57.0, highest: 122.5 123.5 124.5 137.5
> 141.5
> --------------------
> OS windows
> R version 2.10.1 (2009-12-14)
> attached R modules: design+hmisc
> ------------------
> Thank you so much
>
> Peter
>
>
> ______________________________________________
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> 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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