[R] Creating histograms from factors using a for loop

[Sam Player]

# 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

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Room 214 J.R.A. McMillan Building A05
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