[R] Creating histograms from factors using a for loop

[Peter Ehlers]

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?
>