HW1

1.What is the 5th element in the original list of ages?

data1 <- data.table::fread("C:/R-language/BACS/customers.txt")
data1[5]

##    age
## 1:  45

2.What is the fifth lowest age?

library(dplyr)

## 
## 載入套件：'dplyr'

## 下列物件被遮斷自 'package:stats':
## 
##     filter, lag

## 下列物件被遮斷自 'package:base':
## 
##     intersect, setdiff, setequal, union

data1[order(data1$age)][5]

##    age
## 1:  19

3.Extract the five lowest ages together

data2 <- data1[order(data1$age)]
data2[c(1:5)]

##    age
## 1:  18
## 2:  19
## 3:  19
## 4:  19
## 5:  19

4.Get the five highest ages by first sorting them in decreasing order first.

head(data1[order(-data1$age)],5)

##    age
## 1:  85
## 2:  83
## 3:  82
## 4:  82
## 5:  81

5.What is the average (mean) age?

mean(data1$age)

## [1] 46.80702

6.What is the standard deviation of ages?

sd(data1$age)

## [1] 16.3698

7.Make a new variable called age_diff, with the difference between each age and the mean age.

age_diff <-abs(data1$age - mean(data1$age))
head(age_diff,5)

## [1]  2.192982 22.192982  5.807018 26.192982  1.807018

8.What is the average “difference between each age and the mean age”?

mean(age_diff)

## [1] 12.66948

9.Visualize the raw data as we did in class: (a) histogram, (b) density plot, (c) boxplot+stripchart

hist(data1$age)

plot(data1$age, pch = 8,main = "density plot")

boxplot(data1$age,horizontal = TRUE, main = "boxplot + stripchart")
stripchart(data1$age,add = TRUE,method="jitter",col=2, pch=19,at =1.37)