Date: Fri, 23 Jul 2010 23:01:56 -0700
From: Joshua Wiley <jwiley.ps...@gmail.com>
Subject: Re: [R] Trouble retrieving the second largest value from
each row of a data.frame
To: mpw...@illinois.edu
Cc: r-help@r-project.org
Hi,
Here is a little function that will do what you want and return a
nice output:
#Function To calculate top two values and return
my.finder <- function(mydata) {
my.fun <- function(data) {
strongest <- which.max(data)
secondstrongest <- which.max(data[-strongest])
strongestantenna <- names(data)[strongest]
secondstrongantenna <- names(data[-strongest])[secondstrongest]
value <- matrix(c(data[strongest], data[secondstrongest],
strongestantenna, secondstrongantenna), ncol =4)
return(value)
}
dat <- apply(mydata, 1, my.fun)
dat <- t(dat)
dat <- as.data.frame(dat, stringsAsFactors = FALSE)
colnames(dat) <- c("strongest", "secondstrongest",
"strongestantenna", "secondstrongantenna")
dat[ , "strongest"] <- as.numeric(dat[ , "strongest"])
dat[ , "secondstrongest"] <- as.numeric(dat[ , "secondstrongest"])
return(dat)
}
#Using your example data:
yourdata <- structure(list(value0 = c(-13007L, -12838L, -12880L,
-12805L,
-12834L, -11068L, -12807L, -12770L, -12988L, -11779L), value60 =
c(-11707L,
-13210L, -11778L, -11653L, -13527L, -11698L, -14068L, -11665L,
-11736L, -12873L), value120 = c(-11072L, -11176L, -11113L, -11071L,
-11067L, -12430L, -11092L, -11061L, -11137L, -12973L), value180 =
c(-12471L,
-11799L, -12439L, -12385L, -11638L, -12430L, -11709L, -12373L,
-12570L, -12537L), value240 = c(-12838L, -13210L, -13089L, -11561L,
-13527L, -12430L, -11607L, -11426L, -13467L, -12973L), value300 =
c(-13357L,
-13845L, -13880L, -13317L, -13873L, -12814L, -13025L, -12805L,
-13739L, -11146L)), .Names = c("value0", "value60", "value120",
"value180", "value240", "value300"), class = "data.frame",
row.names = c("1",
"2", "3", "4", "5", "6", "7", "8", "9", "10"))
my.finder(yourdata) #and what you want is in a nicely labeled
data frame
#A potential problem is that it is not very efficient
#Here is a test using a matrix of 100,000 rows
#sampled from the same range as your data
#with the same number of columns
data.test <- matrix(
sample(seq(min(yourdata),max(yourdata)), size = 500000, replace =
TRUE),
ncol = 5)
system.time(my.finder(data.test))
#On my system I get
system.time(my.finder(data.test))
user system elapsed
2.89 0.00 2.89
Hope that helps,
Josh
On Fri, Jul 23, 2010 at 6:20 PM, <mpw...@illinois.edu> wrote:
I have a data frame with a couple million lines and want to
retrieve the largest and second largest values in each row,
along with the label of the column these values are in. For
example
row 1
strongest=-11072
secondstrongest=-11707
strongestantenna=value120
secondstrongantenna=value60
Below is the code I am using and a truncated data.frame.
Retrieving the largest value was easy, but I have been getting
errors every way I have tried to retrieve the second largest
value. I have not even tried to retrieve the labels for the
value yet.
Any help would be appreciated
Mike
data<-
data.frame(value0,value60,value120,value180,value240,value300)
data
value0 value60 value120 value180 value240 value300
1 -13007 -11707 -11072 -12471 -12838 -13357
2 -12838 -13210 -11176 -11799 -13210 -13845
3 -12880 -11778 -11113 -12439 -13089 -13880
4 -12805 -11653 -11071 -12385 -11561 -13317
5 -12834 -13527 -11067 -11638 -13527 -13873
6 -11068 -11698 -12430 -12430 -12430 -12814
7 -12807 -14068 -11092 -11709 -11607 -13025
8 -12770 -11665 -11061 -12373 -11426 -12805
9 -12988 -11736 -11137 -12570 -13467 -13739
10 -11779 -12873 -12973 -12537 -12973 -11146
#largest value in the row
strongest<-apply(data,1,max)
#second largest value in the row
n<-function(data)(1/(min(1/(data[1,]-max(data[1,]))))+
(max(data[1,])))
secondstrongest<-apply(data,1,n)
Error in data[1, ] : incorrect number of dimensions
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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.
--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
