R help - Oct 2012 - randomly select another observation with same grouping factor and year value, do for every record in dataframe

Hello,
I am trying to create a function that will move through each record of  a data
frame, find the value in the "HUC" column, then
randomly select another observation from the dataframe with the same value in
"HUC" column, as well as the same value in "Yr" column as
the first observation. I want the function to produce a list of the RchID of the
first observation, the RchID of the second randomly chosen observation, and
several other characteristics of the randomly chosen observation.  Below is the
code I have written, but it doesn't work.

Thanks for any help.
Christy


################test
roads=read.csv("streamland23.csv")

for (i in 1:nrow (roads)){
Sitetype= roads$Sitetype
yr=roads$REACH_Yr
initRchid=roads$RchID
huc1=roads$HUC

sample.df <- function(df, n) df[sample(nrow(df), n), , drop = FALSE]

selected=sample.df(roads[roads$HUC == "huc1"& roads$REACH_Yr
=="yr" , ], 1)


output=cbind (initRchid,selected$RchID,selected$Sitetype,selected$REACH_Yr)

}




Christy Meredith
USDA Forest Service
Rocky Mountain Research Station
PIBO Monitoring
Data Analyst
Voice: 435-755-3573
Fax: 435-755-3563





This electronic message contains information generated by the USDA solely for
the intended recipients. Any unauthorized interception of this message or the
use or disclosure of the information it contains may violate the law and subject
the violator to civil or criminal penalties. If you believe you have received
this message in error, please notify the sender and delete the email
immediately.

	[[alternative HTML version deleted]]

Hello, 
I wrote a request yesterday on how to select a random observation that met
certain criteria. I think mostly I have it  figured out, but I can't figure
out how to append the observations. The output just has one observation in
it. 

Any help would be appreciated, 
thanks.
Christy

setwd ("C:/christy/roads/")
roads=read.csv("streamland23.csv")

for (i in 1:nrow (roads)){
Sitetype= roads$Sitetype[i]
yr=roads$REACH_Yr[i]
initRchid=roads$RchID[i]
huc1=roads$HUC[i]


sample.df <- function(df, n) df[sample(nrow(df), n), , drop = FALSE] 
    
selected=sample.df(roads[roads$HUC == huc1, ], 1) 

selectedb=selected
selectedb$oldrch=initRchid

write.csv(selectedb,file="outhuc3.csv",append=TRUE)

}




--
View this message in context:
http://r.789695.n4.nabble.com/randomly-select-another-observation-with-same-grouping-factor-and-year-value-do-for-every-record-in-e-tp4647351p4647420.html
Sent from the R help mailing list archive at Nabble.com.