R help - Jun 2009 - How to wrap my (working) code in a loop or function? (loop/function newbie alert)

Dear R-helpers,

I have split a dataframe into a list with five elements, with the following
code:
> datalist<-split(data,data$UNIT)
I would now like to run some code (below) on each element of the list to
extract rows from the list elements; then I would like to rbind the
extracted rows into a new dataframe containing all of the extracted rows
from all of the list elements.

I don't need any help with the code itself, it works fine for one chunk of
data (e.g., a single dataframe). The code is:

t0<-match(times$START_DT, data$DATETIME) #MAKE A VECTOR OF START TIMES
t1<-match(times$STOP_DT, data$DATETIME) #MAKE A VECTOR OF STOP TIMES
indices<-mapply(FUN = ":", t0, t1) #MAKES A LIST, EACH ELEMENT
CONTAINS
INDICES OF TIMES CORRESPONDING TO ONE WETLAND
idex<-times[rep(1:nrow(times), sapply(indices, length)),
c("POND_ID","OBS","REP","PID"), drop =
FALSE] #MAKES A DATAFRAME
tm<-data[unlist(indices), ] #FLATTENS THE LIST OF INDICES INTO A DATAFRAME
extracted<-cbind(idex, tm) #BIND IDEX AND TM

But now that I've split my data into a list with five elements, what I
don't
know how to do is wrap my code in a loop or function so I can run it on each
of the five list elements and then rbind the extracted rows together into a
new dataframe.

(What I have now is 5 replicates of the above code, and I would like to
replace that with a loop or function.)

I have spent all morning on this, without much progress, so would appreciate
any help you might be able to provide.

Thanks! Mark Na

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Something like this where you use lapply to pass in each element of the list
to a function and then rbind the result:

datalist <- split(data,data$UNIT)
result <- lapply(datalist, function(.unit){
    t0<-match(times$START_DT, .unit$DATETIME) #MAKE A VECTOR OF START TIMES
    t1<-match(times$STOP_DT, .unit$DATETIME) #MAKE A VECTOR OF STOP TIMES
    indices<-mapply(FUN = ":", t0, t1) #MAKES A LIST, EACH ELEMENT
CONTAINS
INDICES OF TIMES CORRESPONDING TO ONE WETLAND
    idex<-times[rep(1:nrow(times), sapply(indices, length)),
    c("POND_ID","OBS","REP","PID"), drop
= FALSE] #MAKES A DATAFRAME
    tm<-.unit[unlist(indices), ] #FLATTENS THE LIST OF INDICES INTO A
DATAFRAME
    extracted<-cbind(idex, tm) #BIND IDEX AND TM
})
result <- do.call(rbind, result)

On Tue, Jun 30, 2009 at 4:20 PM, Mark Na <mtb954@gmail.com> wrote:
> Dear R-helpers,
>
> I have split a dataframe into a list with five elements, with the following
> code:
>
> > datalist<-split(data,data$UNIT)
>
> I would now like to run some code (below) on each element of the list to
> extract rows from the list elements; then I would like to rbind the
> extracted rows into a new dataframe containing all of the extracted rows
> from all of the list elements.
>
> I don't need any help with the code itself, it works fine for one chunk
of
> data (e.g., a single dataframe). The code is:
>
> t0<-match(times$START_DT, data$DATETIME) #MAKE A VECTOR OF START TIMES
> t1<-match(times$STOP_DT, data$DATETIME) #MAKE A VECTOR OF STOP TIMES
> indices<-mapply(FUN = ":", t0, t1) #MAKES A LIST, EACH ELEMENT
CONTAINS
> INDICES OF TIMES CORRESPONDING TO ONE WETLAND
> idex<-times[rep(1:nrow(times), sapply(indices, length)),
> c("POND_ID","OBS","REP","PID"),
drop = FALSE] #MAKES A DATAFRAME
> tm<-data[unlist(indices), ] #FLATTENS THE LIST OF INDICES INTO A
DATAFRAME
> extracted<-cbind(idex, tm) #BIND IDEX AND TM
>
> But now that I've split my data into a list with five elements, what I
> don't
> know how to do is wrap my code in a loop or function so I can run it on
> each
> of the five list elements and then rbind the extracted rows together into a
> new dataframe.
>
> (What I have now is 5 replicates of the above code, and I would like to
> replace that with a loop or function.)
>
> I have spent all morning on this, without much progress, so would
> appreciate
> any help you might be able to provide.
>
> Thanks! Mark Na
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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