[R] Selecting maximums between different variables

Thu Oct 17 21:17:43 CEST 2013

Hi,

You could also check ?data.table() as it could be faster.

#Speed comparison

set.seed(498) 
oilT <- data.frame(YEAR=rep(rep(1800:2012,50),100),state=rep(rep(state.abb,each=213),100),value=sample(2000:80000,1065000,replace=TRUE),stringsAsFactors=FALSE)
system.time(res1 <- oilT[as.logical(with(oilT,ave(value,list(YEAR),FUN=function(x) x%in% max(x)))),])
# user  system elapsed 
#  0.532   0.008   0.540 
 dim(res1) #as some years have duplicated maximums
#[1] 220   3

 res1[duplicated(res1[,1])|duplicated(res1[,1],fromLast=TRUE),]

library(data.table)
dt1 <- data.table(oilT,key='YEAR')
system.time( res2 <- dt1[dt1[,value %in% max(value),'YEAR']$V1])
#   user  system elapsed 
#  0.060   0.000   0.062 
 res1 <- res1[order(res1$YEAR),]
 row.names(res1) <- 1:nrow(res1)
 identical(res1,as.data.frame(res2))
#[1] TRUE

A.K.

On Thursday, October 17, 2013 1:35 PM, arun <smartpink111 at yahoo.com> wrote:
Hi,
You may try:

unlist(lapply(seq_len(nrow(oil)),function(i) oil[i,-1][which.max(oil[i,-1])])) 
 #  CA    ND 
#40000 60000 
#or
library(reshape2)

datM <- melt(oil,id.var="YEAR")

datM[as.logical(with(datM,ave(value,list(YEAR),FUN= function(x) x%in% max(x)))),]
#  YEAR variable value
#3 2011       CA 40000
#8 2012       ND 60000

A.K.

On Thursday, October 17, 2013 12:50 PM, Tim Umbach <tim.umbach at hufw.de> wrote:
Hi there,

another beginners question, I'm afraid. Basically i want to selct the
maximum of values, that correspond to different variables. I have a table
of oil production that looks somewhat like this:

oil <- data.frame( YEAR = c(2011, 2012),
                   TX = c(20000, 30000),
                   CA = c(40000, 25000),
                   AL = c(20000,
21000),

                   ND = c(21000,60000))

Now I want to find out, which state produced most oil in a given year. I
tried this:

attach(oil)
last_year = oil[ c(YEAR == 2012), ]
max(last_year)

Which works, but it doesnt't give me the corresponding values (i.e. it just
gives me the maximum output, not what state its from).
So I tried this:

oil[c(oil == max(last_year)),]
and this:
oil[c(last_year == max(last_year)),]
and this:
oil[which.max(last_year),]
and this:
last_year[max(last_year),]

None of them work, but they don't give error messages either, the output is
just "NA". The problem is, in my eyes, that I'm comparing the values of
different variables with each other. Because if i change the structure of
the dataframe (which I can't do with the real data, at least not with out
doing it by hand with a huge dataset), it looks like this and works
perfectly:

oil2 <- data.frame (
  names = c('YEAR', 'TX', 'CA', 'AL', 'ND'),
  oil_2011 = c(2011, 20000, 40000, 20000, 21000),
  oil_2012 = c(2012, 30000, 25000, 21000, 60000)
  )
attach(oil2)
oil2[c(oil_2012 == max(oil_2012)),]

Any help is much appreciated.

Thanks, Tim Umbach

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