R help - Jan 2012 - result numeric(0) when using variable1[which(variable2="max(variable2)"]

Dear all,
I have a question about the knowing for which row I have the max value of
one of my variables.
I calculated the Rsquared for different columns and made a list to gather
them. I unlisted this list to create a vector with this values. I want to
know for which column I have the max value of Rsquared.  
The columns were always named in the same way. They always start with
results4$depth_ following by the number. The numbers are constructed as:
seq(1,10,0.1). But if the R squared values are now in 1 column, I don?t know
for which column they are calculated. So I made a new data frame with both
columns:
R2 <- unlist(LIST) 
Cvalue <- c(seq(1,10,0.1)) 
results5 <- data.frame(Cvalue,R2) 

# I know I can calculate the max value of Rsquared by this way: 

max(results5$R2) 

# now I want to know to which Cvalue this belongs. I would write it like
this: 
results5$Cvalue[which(results5$R2 == "max(results5$R2)")] 
# But I always get the solution: 
numeric(0) 
# I don?t know if these Rsquared values are in a kind of format that this
doesn?t work? (I used before for similar things, and I experienced that for
example it cannot works if R recognizes the values as a date).  Maybe
because it?s with a lot of decimals? (eg 2.907530e-01) I know that
max(results5$R2) is in this example 0.6081547 and I can see that that
belongs to the Cvalue == 1.8. It works in the opposite way. 
results5$R2[which(results5$Cvalue == "1.8")] 
# But neither 
results5$Cvalue[which(results5$R2 == "0.6081547")] 
# nor 
results5$Cvalue[which(results5$R2 == "max(results5$R2)")] 
# works?

I hope someone can help me with this problem
Kind regards
Nerak

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On 17/01/2012 5:35 AM, Nerak wrote:
> Dear all,
> I have a question about the knowing for which row I have the max value of
> one of my variables.
> I calculated the Rsquared for different columns and made a list to gather
> them. I unlisted this list to create a vector with this values. I want to
> know for which column I have the max value of Rsquared.
> The columns were always named in the same way. They always start with
> results4$depth_ following by the number. The numbers are constructed as:
> seq(1,10,0.1). But if the R squared values are now in 1 column, I don?t
know
> for which column they are calculated. So I made a new data frame with both
> columns:
> R2<- unlist(LIST)
> Cvalue<- c(seq(1,10,0.1))
> results5<- data.frame(Cvalue,R2)
>
> # I know I can calculate the max value of Rsquared by this way:
>
> max(results5$R2)
>
> # now I want to know to which Cvalue this belongs. I would write it like
> this:
> results5$Cvalue[which(results5$R2 == "max(results5$R2)")]
Don't use quotes on the expression.  None of your R2 values are the string

"max(results5$R2)"

which is why you're getting numeric(0).

You can also make it simpler by using the which.max() function.

Duncan Murdoch
> # But I always get the solution:
> numeric(0)
> # I don?t know if these Rsquared values are in a kind of format that this
> doesn?t work? (I used before for similar things, and I experienced that for
> example it cannot works if R recognizes the values as a date).  Maybe
> because it?s with a lot of decimals? (eg 2.907530e-01) I know that
> max(results5$R2) is in this example 0.6081547 and I can see that that
> belongs to the Cvalue == 1.8. It works in the opposite way.
> results5$R2[which(results5$Cvalue == "1.8")]
> # But neither
> results5$Cvalue[which(results5$R2 == "0.6081547")]
> # nor
> results5$Cvalue[which(results5$R2 == "max(results5$R2)")]
> # works?
>
> I hope someone can help me with this problem
> Kind regards
> Nerak
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/result-numeric-0-when-using-variable1-which-variable2-max-variable2-tp4302887p4302887.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at 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.

On 17-01-2012, at 11:35, Nerak wrote:
> Dear all,
> I have a question about the knowing for which row I have the max value of
> one of my variables.
> I calculated the Rsquared for different columns and made a list to gather
> them. I unlisted this list to create a vector with this values. I want to
> know for which column I have the max value of Rsquared.  
> The columns were always named in the same way. They always start with
> results4$depth_ following by the number. The numbers are constructed as:
> seq(1,10,0.1). But if the R squared values are now in 1 column, I don?t
know
> for which column they are calculated. So I made a new data frame with both
> columns:
> R2 <- unlist(LIST) 
> Cvalue <- c(seq(1,10,0.1)) 
> results5 <- data.frame(Cvalue,R2) 
> 
> # I know I can calculate the max value of Rsquared by this way: 
> 
> max(results5$R2) 
> 
> # now I want to know to which Cvalue this belongs. I would write it like
> this: 
> results5$Cvalue[which(results5$R2 == "max(results5$R2)")] 
> # But I always get the solution: 
> numeric(0) 
You haven't provided a reproducible example.
So I tried this

set.seed(1)
x <- round(runif(10),3)
x
which.max(x)
which(x==max(x))
x
which(x=="0.945")
which(x==max(x))
which(x=="max(x)")
x[which(x=="max(x)")]

If you run this you will see that the last line results in numeric(0).

So; why are you using quotes in the which expression? Is results5$R2 a character
string?
This should work

results5$Cvalue[which(results5$R2 == max(results5$R2))]

But this is shorter

results5$Cvalue[which.max[results5$R2)]

Berend