How to draw histograms in r - r

Question

My code is reading in a file which looks like this:
Wafer Analyses
%HN20396815 150.000000 03/27/2016 04:06:27
Vf2 Site
2.76 1
2.32 2
2.56 3
2.45 2
2.76 4
2.98 3
2.58 1
2.42 2
2.76 1
2.32 4
2.56 3
2.45 2
2.76 4
2.98 3
2.58 1
2.42 2
then I segregate "Vf2" data by "Site" and plot for each site in a histogram, however the histogram doesn't get printed out, how do I rectify this? This is my code>
blufile <- read.table("C:/blufiles/WFRHN20396815_700.blu", skip = 2, header = TRUE, sep="\t")
Vf2 = blufile["Vf2"]
Site = blufile["Site"]
blufile2 <- data.frame(Vf2, Site)
blufile2$Vf2[blufile2$Site == '2']
set.seed(42)
p1 <- blufile2$Vf2[blufile2$Site == '1'] # centered at 4
p2 <- blufile2$Vf2[blufile2$Site == '2'] # centered at 6
p3 <- blufile2$Vf2[blufile2$Site == '3'] # centered at 4
p4 <- blufile2$Vf2[blufile2$Site == '4'] # centered at 6
plot( p1, col=rgb(0,0,1,1/4), xlim=c(0,4)) # first histogram
plot( p2, col=rgb(1,0,0,1/4), xlim=c(0,4), add=T) # second
plot( p3, col=rgb(0,1,0,1/4), xlim=c(0,4), add=T) # first histogram
plot( p4, col=rgb(1,1,0,1/4), xlim=c(0,4), add=T) # second
I want a similar output ->

Answer 1

The solution #alistaire have provided worked with the data you have provided.
ggplot(df, aes(x=Vf2)) +
geom_histogram(bins=5) +
facet_wrap(~Site)
The data df used in this case is:
structure(list(Vf2 = c(2.76, 2.32, 2.56, 2.45, 2.76, 2.98, 2.58,
2.42, 2.76, 2.32, 2.56, 2.45, 2.76, 2.98, 2.58, 2.42), Site = c(1L,
2L, 3L, 2L, 4L, 3L, 1L, 2L, 1L, 4L, 3L, 2L, 4L, 3L, 1L, 2L)), .Names = c("Vf2",
"Site"), class = "data.frame", row.names = c(NA, -16L))
Please elaborate more on your issues if this still do not work.
EDIT:
The issue with your code is that you used plot which would result in a x,y point plot, instead of hist.
Here's a solution with base:
df_list <- split(df, df$Site) #produce a list of 4 data.frame, each with one level of Site
dev.off() # close existing output on console
for(i in 1:length(df_list)){
dat <- df_list[[i]]$Vf2 # select Vf2 data from site i
hist_col <- c(rgb(0,0,1,1/4), rgb(1,0,0,1/4), rgb(0,1,0,1/4), rgb(1,1,0,1/4))[i] # select rgb colour for site i plot
hist(dat, col=hist_col, xlim=c(0,4), ylim=c(0, 5)) #plot histogram for each site
par(new=T) # add new histogram layer on top
}
The solution for ggplot is slightly more confusing in this case:
ggplot(data=df, aes(x=Vf2, fill=factor(Site), colour=factor(Site))) +
geom_histogram(data=df %>% filter(Site==1), bins=5, alpha=.5) +
geom_histogram(data=df %>% filter(Site==2), bins=5, alpha=.5) +
geom_histogram(data=df %>% filter(Site==3), bins=5, alpha=.5) +
geom_histogram(data=df %>% filter(Site==4), bins=5, alpha=.5) +
theme_bw()