R help - Jun 2011 - Linking 2 columns in 2 databases and applying a function

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

	[[alternative HTML version deleted]]

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
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> 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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Daniel,

That indeed does work... and I didn't even need to learn a new function.
Thanks!

-- 

Ryan Utz, Ph.D.
Aquatic Ecologist/STREON Scientist
National Ecological Observatory Network

Home/Cell: (724) 272-7769
Work: (720) 746-4844 ext. 2488

	[[alternative HTML version deleted]]