error:max not meaningful for factors

Hello,

I run this script , because i would like to do the mean of x and y base 

on

alpha as factor.


library(xlsx)
library(ROCR
filename<-"amanhecer roc.csv"
rocdata<- read.table(filename, sep=";",header=TRUE,dec=",")

rocdata$alpha.15_12 <- as.factor(rocdata$alpha.15_12)

TPaverage <- tapply(rocdata$y.15_12, rocdata$alpha.15_12, mean)
FPaverage <- tapply(rocdata$x.15_12, rocdata$alpha.15_12, mean)

###And them with the new data i want to create a plot, kind of ROC 

plot.

 Anthias<-rocdata
 str(Anthias)
data(ROCR.simple)
pred <- prediction( ROCR.simple$predictions, ROCR.simple$labels )
perf <- performance( pred, "tpr", "fpr" )
windows(width = 9.5, height = 10.50)
par(mfrow = c(1,1))

cc<-Anthias[1]
ee<-Anthias[2]
aa<-Anthias[3]
perf at x.name<-"FP"
perf at y.name<-"TP"
perf at alpha.name<-"Speed"
bb<-data.frame(aa)
perf at x.values<-bb
dd<-data.frame(cc)
perf at y.values<-dd
ff<-data.frame(ee)
perf at alpha.values<-ff

plot(perf, main="Teste", colorize=TRUE, 

coloraxis.at=c(0,2,4,6,8,10),

 coloraxis.cex.axis=0.8, colorize.palette=(rainbow(256,start=0, 

end=0.7)),

lwd=7, colorkey.relwidth=0.4, yaxis.las=1)

But after run the whole script i got the error:max not meaningful for
factors, anyone can help me?  I am a beginner in R ,so sorry if this is
wasting anyone's time*.*

Hi Marta,
The error message is straightforward. Somewhere in one of the 
functions you have called, the "max" function is applied to your factor 
variable. The definition of factor variables is that the the actual values 
are of nominal class, in which there is no meaningful ordering of 
values, therefore the maximum value is undefined. You could try 
as.numeric(alpha), but that is dangerous as it depends on whether the 
sorting of values (default alphabetic) is what you want. If we knew what 
"alpha" was, it would help.

Jim

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Hi

Not much helpful. Now we know what you ***think*** alpha is but not what it really is.

You shall post at least result of

str(your.objects)

I also wonder why do you populate slots in perf manually and with data.frames instead of lists which are required according to documentation.

Regards
Petr

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Marta valdes lopez
Sent: Thursday, July 03, 2014 12:35 PM
To: r-help at r-project.org
Subject: Re: [R] error:max not meaningful for factors

Thank you Jim for your answer.Ok alpha( it is the speed of the boat) is
a range of number from 0.5 to 10 like 0.5,1,1.5,2...., I would like to
have the mean of x and y base on each value of alpha, because I have
like ten numbers of x for each value of speed, thats why I want the
mean of that and them i could create the roc plot with the new values.
I would say that alpha values are ordered already?

Thanks , Marta



2014-07-03 1:17 GMT+02:00 Jim Lemon <jim at bitwrit.com.au>:

On Wed, 2 Jul 2014 02:42:31 PM Marta valdes lopez wrote:

Hello,

I run this script , because i would like to do the mean of x and y
base

on

alpha as factor.


library(xlsx)
library(ROCR
filename<-"amanhecer roc.csv"
rocdata<- read.table(filename, sep=";",header=TRUE,dec=",")

rocdata$alpha.15_12 <- as.factor(rocdata$alpha.15_12)

TPaverage <- tapply(rocdata$y.15_12, rocdata$alpha.15_12, mean)
FPaverage <- tapply(rocdata$x.15_12, rocdata$alpha.15_12, mean)

###And them with the new data i want to create a plot, kind of ROC

plot.

 Anthias<-rocdata
 str(Anthias)
data(ROCR.simple)
pred <- prediction( ROCR.simple$predictions, ROCR.simple$labels )
perf <- performance( pred, "tpr", "fpr" ) windows(width = 9.5,
height = 10.50) par(mfrow = c(1,1))

cc<-Anthias[1]
ee<-Anthias[2]
aa<-Anthias[3]
perf at x.name<-"FP"
perf at y.name<-"TP"
perf at alpha.name<-"Speed"
bb<-data.frame(aa)
perf at x.values<-bb
dd<-data.frame(cc)
perf at y.values<-dd
ff<-data.frame(ee)
perf at alpha.values<-ff

plot(perf, main="Teste", colorize=TRUE,

coloraxis.at=c(0,2,4,6,8,10),

 coloraxis.cex.axis=0.8, colorize.palette=(rainbow(256,start=0,

end=0.7)),

lwd=7, colorkey.relwidth=0.4, yaxis.las=1)

But after run the whole script i got the error:max not meaningful
for factors, anyone can help me?  I am a beginner in R ,so sorry if
this is wasting anyone's time*.*

Hi Marta,
The error message is straightforward. Somewhere in one of the
functions you have called, the "max" function is applied to your
factor variable. The definition of factor variables is that the the
actual values are of nominal class, in which there is no meaningful
ordering of values, therefore the maximum value is undefined. You
could try as.numeric(alpha), but that is dangerous as it depends on
whether the sorting of values (default alphabetic) is what you want.
If we knew what "alpha" was, it would help.

Jim

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Thank you Jim for your answer.Ok alpha( it is the speed of the boat) is 

a

range of number from 0.5 to 10 like 0.5,1,1.5,2...., I would like to have
the mean of x and y base on each value of alpha, because I have like 

ten

numbers of x for each value of speed, thats why I want the mean of 

that and

them i could create the roc plot with the new values.
I would say that alpha values are ordered already?

Thanks , Marta

Hi Marta,
The variable "alpha" should be numeric and shouldn't cause the error 
you described. If you get this result:

is.numeric(alpha)
FALSE

then "alpha" has been converted to a factor somehow. This usually 
happens when one or more values of alpha can't be read as a number in 
the read.csv step. It doesn't seem like your dataset is very large, so 
perhaps you could print alpha:

alpha

and see if anything doesn't look like a number. You may be able to track 
this back to the CSV file and correct a typo or something.

Jim