R help - Sep 2009 - Creating histograms from factors using a for loop

# I have a dataframe with data and factors similar to the following:

a <- rep(c("a", "b"), c(6,6))
df <- data.frame(f=a, d=rnorm(12))
df

# I am trying to write a 'for' loop which will produce a jpeg histogram 
for each factor. I can individually isolate the data from a factor and 
produce a jpeg histogram like so:

fnc <- function(x){
         x <- df[df$f=="a", "d"]
}

y <- fnc(df[df$f=="a", "d"])

jpeg(filename="foo.jpeg")
hist(y)
dev.off()

# I'm having trouble creating a loop repeating the process for all the 
other factors. The following is the best I could come up with. It 
produces a single jpeg histogram of the first factor titled with a list 
of all the factors.

a <- rep(c("a", "b"), c(6,6))
df <- data.frame(f=a, d=rnorm(12))
df

for (i in levels(df[,"f"])){
         y <- df[df$f==i, 2]
         jpeg(filename=(levels(df[i,"f"])))
         hist(y, main=levels(df[i,"f"]))
         dev.off()
         }

# I'm obviously not understanding how loops work with factors. Can 
anybody point me in the right direction?

-- 
Sam Player, B.Sc.(Hons.) B.A.
Ph.D. Candidate, Faculty of Agriculture, Food & Natural Resources,
University of Sydney

Email: splayer at usyd.edu.au

Agroecosystems Research Group
Room 214 J.R.A. McMillan Building A05
University of Sydney NSW 2006, Australia

Angkor Research Program
Room 305 Old Teachers College A22
University of Sydney NSW 2006, Australia

Sam,

Your loop produces two jpegs but the second overwrites the first.
What do you expect

   levels(df[i,"f"])

to produce? (Think about it.)

Try

  jpeg(filename=paste(i,".jpg",sep=""))

and you may want to fix the titles as well.

Peter

Sam Player wrote:
> # I have a dataframe with data and factors similar to the following:
> 
> a <- rep(c("a", "b"), c(6,6))
> df <- data.frame(f=a, d=rnorm(12))
> df
> 
> # I am trying to write a 'for' loop which will produce a jpeg
histogram
> for each factor. I can individually isolate the data from a factor and 
> produce a jpeg histogram like so:
> 
> fnc <- function(x){
>         x <- df[df$f=="a", "d"]
> }
> 
> y <- fnc(df[df$f=="a", "d"])
> 
> jpeg(filename="foo.jpeg")
> hist(y)
> dev.off()
> 
> # I'm having trouble creating a loop repeating the process for all the 
> other factors. The following is the best I could come up with. It 
> produces a single jpeg histogram of the first factor titled with a list 
> of all the factors.
> 
> a <- rep(c("a", "b"), c(6,6))
> df <- data.frame(f=a, d=rnorm(12))
> df
> 
> for (i in levels(df[,"f"])){
>         y <- df[df$f==i, 2]
>         jpeg(filename=(levels(df[i,"f"])))
>         hist(y, main=levels(df[i,"f"]))
>         dev.off()
>         }
> 
> # I'm obviously not understanding how loops work with factors. Can 
> anybody point me in the right direction?
>

On Sep 19, 2009, at 5:37 AM, Sam Player wrote:
> # I have a dataframe with data and factors similar to the following:
>
> a <- rep(c("a", "b"), c(6,6))
> df <- data.frame(f=a, d=rnorm(12))
> df
>
> # I am trying to write a 'for' loop which will produce a jpeg  
> histogram for each factor. I can individually isolate the data from  
> a factor and produce a jpeg histogram like so:
>
> fnc <- function(x){
>        x <- df[df$f=="a", "d"]
> }
>
> y <- fnc(df[df$f=="a", "d"])
>
> jpeg(filename="foo.jpeg")
> hist(y)
> dev.off()
>
> # I'm having trouble creating a loop repeating the process for all  
> the other factors. The following is the best I could come up with.  
> It produces a single jpeg histogram of the first factor titled with  
> a list of all the factors.
>
> a <- rep(c("a", "b"), c(6,6))
> df <- data.frame(f=a, d=rnorm(12))
> df
>
> for (i in levels(df[,"f"])){
>        y <- df[df$f==i, 2]
>        jpeg(filename=(levels(df[i,"f"])))
>        hist(y, main=levels(df[i,"f"]))
>        dev.off()
>        }
You are a bit unclear about what you are seeking but if you want  
separate file names and titles that are factor-specifich, then why not  
use "i" inside the loop as itself?

for (i in levels(df[,"f"])){
        y <- df[df$f==i, 2]
        jpeg(filename=paste("file_",i,sep=""))
        hist(y, main=paste("Factor =",i,sep=""))
        dev.off()
        }
>
> # I'm obviously not understanding how loops work with factors.
It seems that you are unclear about loop indices. You are not really  
passing factors anyway, but rather elements of a character vector,  
levels(df[,"f"]).
> Can anybody point me in the right direction?
>
> -- 
> Sam Player, B.Sc.(Hons.) B.A.
> Ph.D. Candidate, Faculty of Agriculture, Food & Natural Resources,  
> University of Sydney
>
> Email: splayer at usyd.edu.au
>
> Agroecosystems Research Group
> Room 214 J.R.A. McMillan Building A05
> University of Sydney NSW 2006, Australia
>
> Angkor Research Program
> Room 305 Old Teachers College A22
> University of Sydney NSW 2006, Australia
>
> ______________________________________________
> 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.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

You could plot both histograms into the same file using this:
library(lattice)
jpeg(filename="combined.jpeg")
histogram(~d|f, data = df)
dev.off()

Schalk Heunis


On Sat, Sep 19, 2009 at 11:37 AM, Sam Player <samtplayer@gmail.com> wrote:
> # I have a dataframe with data and factors similar to the following:
>
> a <- rep(c("a", "b"), c(6,6))
> df <- data.frame(f=a, d=rnorm(12))
> df
>
> # I am trying to write a 'for' loop which will produce a jpeg
histogram for
> each factor. I can individually isolate the data from a factor and produce
a
> jpeg histogram like so:
>
> fnc <- function(x){
>        x <- df[df$f=="a", "d"]
> }
>
> y <- fnc(df[df$f=="a", "d"])
>
> jpeg(filename="foo.jpeg")
> hist(y)
> dev.off()
>
> # I'm having trouble creating a loop repeating the process for all the
> other factors. The following is the best I could come up with. It produces
a
> single jpeg histogram of the first factor titled with a list of all the
> factors.
>
> a <- rep(c("a", "b"), c(6,6))
> df <- data.frame(f=a, d=rnorm(12))
> df
>
> for (i in levels(df[,"f"])){
>        y <- df[df$f==i, 2]
>        jpeg(filename=(levels(df[i,"f"])))
>        hist(y, main=levels(df[i,"f"]))
>        dev.off()
>        }
>
> # I'm obviously not understanding how loops work with factors. Can
anybody
> point me in the right direction?
>
> --
> Sam Player, B.Sc.(Hons.) B.A.
> Ph.D. Candidate, Faculty of Agriculture, Food & Natural Resources,
> University of Sydney
>
> Email: splayer@usyd.edu.au
>
> Agroecosystems Research Group
> Room 214 J.R.A. McMillan Building A05
> University of Sydney NSW 2006, Australia
>
> Angkor Research Program
> Room 305 Old Teachers College A22
> University of Sydney NSW 2006, Australia
>
> ______________________________________________
> 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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