[R] R matching lat/lon pairs from two datasets?

[Don MacQueen]

I guess you want the subset of "data" whose lat/long pairs are 
present in "data2"?

Try renaming your columns so that V1 and V2 are the same in both data 
frames (either lat,long, or long,lat, but not one way in one 
dataframe and the other way in the other one.

Then use merge()

-Don

At 5:37 PM -0700 1/4/10, Douglas M. Hultstrand wrote:
>Hello,
>
>I am trying to match lat/lon from one dataset with the lat/lon from 
>a second dataset and use that rows data for calculations.  I am 
>using match, but this is finding the first match and not comparing 
>the pair, how can I determine if the lat/lon are the same?  See 
>example below.  Is there a better way to determine to a matching 
>pair of lat/lon values?
>
>Example Datasets:
>>  data2
>       V1    V2 V3
>1 -123.76 47.82  8
>2 -123.75 47.82 11
>
>>  data[1:2]
>      V1      V2
>1  47.82 -123.76
>2  47.82 -123.75
>3  47.82 -123.74
>4  47.82 -123.73
>
>#Subset of current R code :
>lat <- data$V1
>lon <- data$V2
>yrs <- c(1,2,5,10,25,50,100,200,500,1000)
>lon2 <- data2$V1
>lat2 <- data2$V2
>ppt2 <- data2$V3
>
>for(i in 1:length(lat2)) {
>        loc <- match(lat2[i],lat)
>        loc2 <- match(lon2[i], lon)
>        print(loc); print(loc2)
>
>        #Need to test to make sure loc equals loc2
>        freq_ppt <- 
>c(data[i,4],data[i,6],data[i,8],data[i,10],data[i,12],data[i,14],data[i,16],data[i,18],data[i,20],data[i,22])
>        print(freq_ppt)
>        return_value <- approx(freq_ppt,yrs,xout=data2[i,3])
>        print(return_value)
>}
>
>
>Thanks for your help,
>Doug
>
>--
>---------------------------------
>Douglas M. Hultstrand, MS
>Senior Hydrometeorologist
>Metstat, Inc. Windsor, Colorado
>voice: 970.686.1253
>email: dmhultst at metstat.com
>web: http://*www.*metstat.com
>
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>R-help at r-project.org mailing list
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>PLEASE do read the posting guide http://*www.*R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.


-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062