Re: [R] Trouble retrieving the second largest value from each row of a data.frame

Sat, 24 Jul 2010 17:11:04 -0700 


On Jul 24, 2010, at 4:54 PM, <mpw...@illinois.edu> wrote:


THANKS, but I have one issue and one question.
For some reason the "secondstrongest" value for row 3 and 6 are incorrect (they are the strongest) the remaining 10 are correct??
In my run of Wiley's code I instead get identical values for rows 2,5,6. Holtman's and my solutions did not suffer from that defect, although mine suffered from my misreading of your request, thinking that you wanted the top 3. The fix is trivial
These data are being used to track radio-tagged birds, they are from automated radio telemetry receivers. I will applying the following formula 

  diff <- ((strongest- secondstrongest)/100)
  bearingdiff <-30-(-0.0624*(diff**2))-(2.8346*diff)
vals <- c("value0", "value60", "value120", "value180", "value240", "value300") 
value.str2 <- (match(yourdata$secondstrongestantenna, vals)-1)*60
value.str1 <- (match(yourdata$strongestantenna, vals)-1)*60
change.ind <- abs(match(yourdata, vals) - which(match(yourdata, vals) )
A) Then the bearing diff is added to strongestantenna (value0 = 0degrees) if the secondstrongestatenna is greater (eg value0 and value60),
B) or if the secondstrongestantenna is smaller than the strongestantenna, 
then the bearingdiff is substracted from the strongestantenna.
C) The only exception is that if value0 (0degrees) is strongest and value300(360degrees) is the secondstrongestantenna then the bearing is 360-bearingdiff.
D) Also the strongestantenna and secondstrongestantenna have to be next to each other (e.g. value0 with value60, value240 with value300, value0 with value300) or the results should be NA. 

After setting finalbearing with A, B, and C then:
yourdata$finalbearing <- with(yourdata, ifelse (
                                change.ind <5 & change.ind > 1 ,
                                             NA, finalbearing) )
I have been trying to use a series of if,else statements to produce these bearing, but all I am producing is errors. Any suggestion would be appreciated. 




Again THANKS for you efforts.

Mike

---- Original message ----

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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--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/


______________________________________________
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
and provide commented, minimal, self-contained, reproducible code.


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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.

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