[R] Linking 2 columns in 2 databases and applying a function

[Daniel Malter]

For example, you can merge the two data frames and do a direct comparison:

df<-merge(x,y,all.x=T,all.y=F)
df
df$Q>df$Threshold_Q

HTH,
Daniel 


Ryan Utz-2 wrote:
> 
> Hi all,
> 
> I have two datasets, one that represents a long-term time series and one
> that represents summary data for the time series. It looks something like
> this:
> 
> x<-data.frame(Year=c(2001,2001,2001,2001,2001,2001,2002,2002,2002,2002,2002,2002),
> Month=c(1,1,1,2,2,2),Q=c(5,5,5,6,6,6,3,3,3,4,4,5))
> y<-data.frame(Year=c(2001,2001,2002,2002),Month=c(1,2,1,2),Threshold_Q=c(5,5,4,4))
> 
> What I'd like to do is link the Year and Month fields in both dataframes
> then determine if Q exceeds Q_Threshold (by noting it with something like
> 1
> or 0 in a new field in the dataframe x).
> 
> If I were doing this in the more-familiar-to-me Matlab, I'd just write a
> pair of nested for-loops. But as we know, this won't fly in R. I've tried
> reading the help pages and seeking for solutions on the net, with no luck
> (I'm relatively new to R and the help pages are still a bit opaque to me).
> It seems like the functions "apply" or "lapply" are key, but I can't make
> sense of their syntax.
> 
> Any advice/help?!?
> 
> Many thanks,
> Ryan
> 
> -- 
> 
> Ryan Utz, Ph.D.
> Aquatic Ecologist/STREON Scientist
> National Ecological Observatory Network
> 
> Home/Cell: (724) 272-7769
> Work: (720) 746-4844 ext. 2488
> 
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> 
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