如何在时间序列数据框中获取汇总表/箱线图？

Question

I have a data frame which contains time sequence, like this:

example <- data.frame(
Date=seq(
 from=as.POSIXct("2012-1-1 0:00", tz="UTC"),
 to=as.POSIXct("2012-1-31 23:00", tz="UTC"),
 by="10 min"),
 frequency=runif(4459, min=12, max=26))

I would like count min value, mean, max value etc. (using summary table) by days: for example summary table of days 2012 1. 1. (using only the first 144 raws), 2012 1. 2. (using raws from 145 to 288), 2012 1. 3. (using raws from 289 to 432) etc.

how can I get this table? I have tried this

summary(example$freqency, example$Date, by="day")

how can I draw dropbox for every day separately? I have tried this:

boxplot(example$freqency, example$Date, by="day")

How can I select time data within days? I also want to calculate summary table by days, but in this case I want to use only data in every hours (eg 0:00, 1:00, 2:00 etc.)

Can somebody help me?

Answer 1

To get summary of frequency by day, you could use aggregate from base R in combination with strftime() :

aggregate(frequency ~ strftime(Date, "%d"),
          FUN = summary, data = example)

To get a boxplot per day, we just need to create a $day column for the x-axis in ggplot2 .

library(ggplot2)
example$day <- strftime(example$Date, "%d")
ggplot(example, aes(x = factor(day), y = frequency)) + geom_boxplot()

Answer 2

Try this simply:

within days:

example$str.date <- substring(as.character(example$Date),1,10)
summary.example <- aggregate(frequency~str.date, example, FUN = summary)
library(ggplot2)
ggplot(example, aes(str.date, frequency, group=str.date, fill=str.date)) + geom_boxplot()  + 
  theme(axis.text.x = element_text(angle=90, vjust = 0.5))

within hours (within each day):

example$str.date.hrs <- substring(as.character(example$Date),1,13)
summary.example <- aggregate(frequency~str.date.hrs, example, FUN = summary)
library(ggplot2)
ggplot(example[example$str.date=='2012-01-01',], aes(str.date.hrs, frequency, group=str.date.hrs, fill=str.date.hrs)) + geom_boxplot()  + 
  theme(axis.text.x = element_text(angle=90, vjust = 0.5))