box plot for multiple observations - r

Question

I have multiple observation of rainfall for the same station for around 14 years the data frame is in something like this :
df (from date -01/01/2000)
v1 v2 v3 v4 v5 v6 ........ v20
1 1 2 4 8 9..............
1.4 4 3.8..................
1.5 3 1.6....................
1.6 8 .....................
.
.
.
.
till date 31/01/2013 i.e total 5114 observations
where v1 v2 ...v20 are the rainfall simulation for the same point; I want to plot the box plot which represents the collective range of quantiles and median monthly when all the observations are taken together.
I can plot box plot for single monthly values using :
df$month<-factor(month.name,levels=month.name)
library(reshape2)
df.long<-melt(df,id.vars="month")
ggplot(df.long,aes(month,value))+geom_boxplot()
but in this problem as the data is daily and there are multiple observations i don't get idea where to start.
sample data
df = data.frame(matrix(rnorm(20), nrow=5114,ncol=100))
In case if u want to work with a zoo object :
date<-seq(as.POSIXct("2000-01-01 00:00:00","GMT"),as.POSIXct("2013-12-31 00:00:00","GMT"), by="1440 min")
If you want yo can also convert it to zoo object
x <- zoo(df, order.by=seq(as.POSIXct("2000-01-01 00:00:00","GMT"), as.POSIXct("2013-12-31 00:00:00","GMT"), by="1440 min"))

Answer 1

I am not familiar with zoo. So, I converted your sample to data frame. Your idea of using melt() is a right way. Then, you need to aggregate rain amount by month. I think it is good to look up aggregate() and other options. Here, I used dplyr and tidyr to arrange the sample data. I hope this will let you move forward.
### zoo to data frame by # Joshua Ulrich
### http://stackoverflow.com/questions/14064097/r-convert-between-zoo-object-and-data-frame-results-inconsistent-for-different
zoo.to.data.frame <- function(x, index.name="Date") {
stopifnot(is.zoo(x))
xn <- if(is.null(dim(x))) deparse(substitute(x)) else colnames(x)
setNames(data.frame(index(x), x, row.names=NULL), c(index.name,xn))
}
### to data frame
foo <- zoo.to.data.frame(df)
str(foo)
library(dplyr)
library(tidyr)
### wide to long data frame, aggregate rain amount by Date
ana <- foo %>%
melt(., id.vars = "Date") %>%
group_by(Date) %>%
summarize(rain = sum(value))
### Aggregate rain amount by year and month
bob <- ana %>%
separate(Date, c("year", "month", "date")) %>%
group_by(year, month) %>%
summarize(rain = sum(rain))
### Drawing a ggplot figure
ggplot(data = bob, aes(x = month, y = rain)) +
geom_boxplot()

Answer 2

just found out an easier way to do it, hwoever your answered really helped jazzuro
install.packages("reshape2")
library(dplyr)
library(reshape2)
require(ggplot2)
df = data.frame(matrix(rnorm(20), nrow=5114,ncol=100))
x <- zoo(df, order.by=seq(as.POSIXct("2000-01-01 00:00:00","GMT"),
as.POSIXct("2013-12-31 00:00:00","GMT"), by="1440 min"))
v<-aggregate(x, as.yearmon, mean)
months<- rep(1:12,14)
lol<-data.frame(v,months)
df.m <- melt(lol, id.var = "months")
View(df.m)
p <- ggplot(df.m, aes(factor(months), value))
p + geom_boxplot(aes(fill = months))