R 基础知识：数据结构（list & factor）

R语言中基本的数据单位是向量（vector），通过对于向量的堆叠我们能组合出更进阶的数据结构。这些数据结构包括弹性容器：list；有阶阶层的向量：factor；数据框：data.frame；二维的向量：matrix；阵列：array。

1. list

若我们用向量c()存储数据，因为其中有文字向量，所以在所有数据都会变成文字向量。

# 以朱元璋为例
name = "zhuyuanzhang"
nickname = c("zhuchongba","zhuguorui","zhubaba")
gender = "man"
profession = "emperor"
birthAndDead = "1328-1398"
age = 70
zyz = c(name,nickname,gender,profession,birthAndDead,age)
zyz

# [1] "zhuyuanzhang" "zhuchongba"   "zhuguorui"   
# [4] "zhubaba"      "man"          "emperor"     
# [7] "1328-1398"    "70"          

若我们用list来储存，将宣告好的不同数据存储进去。我们可以看到list的强大收纳能力，他用数个[[索引值]]将各个向量依序放入其中。在list中各个向量依然保有自己的类型。

zyzList = list(name,nickname,gender,profession,birthAndDead,age)
zyzList
# [[1]]
# [1] "zhuyuanzhang"
# [[2]]
# [1] "zhuchongba" "zhuguorui"  "zhubaba"   
# [[3]]
# [1] "man"
# [[4]]
# [1] "emperor"
# [[5]]
# [1] "1328-1398"
# [[6]]
# [1] 70

# 查看各个数据的类型
str(zyzList) 
# List of 6
#  $ : chr "zhuyuanzhang"
#  $ : chr [1:3] "zhuchongba" "zhuguorui" "zhubaba"
#  $ : chr "man"
#  $ : chr "emperor"
#  $ : chr "1328-1398"
#  $ : num 70

list中选取数据的时候可以用[[索引值]]、[[“名称”]]和$名称。

# 上方的list只能有[[索引值]]来查找，因为我们没有给各个变数命名
zyzList[[2]][2]
# [1] "zhuguorui

# 增加下变数名称,就可以用[[“名称”]]和$名称来查找数据了
zyzListPro = list(Name = name,
                  Nickname = nickname,
                  Gender = gender,
                  Profession = profession,
                  BandD = birthAndDead,
                  Age = age)
zyzListPro[["Nickname"]]
zyzListPro[["Nickname"]][1]
zyzListPro$Nickname
zyzListPro$Nickname[1]
# [1] "zhuchongba" "zhuguorui"  "zhubaba"   
# [1] "zhuchongba"
# [1] "zhuchongba" "zhuguorui"  "zhubaba"   
# [1] "zhuchongba"

# 可以任意组合提取
sprintf("%s is a %s, maybe his age is %.2f",
        zyzListPro$Name,
        zyzListPro$Profession,
        zyzListPro$Age*2)
# [1] "zhuyuanzhang is a emperor, maybe his age is 140.00"

1.factor

R语言中很独特的一个数据结构就是factor。他是一种有阶层的向量（levels），一般叫他因子或是因素向量。

fourSeasons = c("spring", "summer", "autumn", "winter")
class(fourSeasons) # 文字向量
# [1] "character"

fourSeasonsFactor = factor(fourSeasons)
fourSeasonsFactor
class(fourSeasonsFactor) # 因子
# [1] spring summer autumn winter
# Levels: autumn spring summer winter
# [1] "factor"

预设的阶层（lever）是以A-Z的字母排序的（Levels: autumn spring summer winter），不过设置factor中的参数ordered = TRUE 与 levels = ，就可以根据自己的偏好做排序。

fourSeasonsFactor = factor(fourSeasons,ordered = TRUE,levels = c("summer", "winter", "spring", "autumn"))
fourSeasonsFactor
# [1] spring summer autumn winter
# Levels: summer < winter < spring < autumn

Console印出的lever会按照大小关系做排序，所以factor很适合用在有隐含顺序意义的文字向量。

temperatures = c("warm", "hot", "cold")
temperaturesFactor = factor(temperatures, ordered = TRUE, levels = c("cold", "warm", "hot"))
temperaturesFactor
# [1] warm hot  cold
# Levels: cold < warm < hot

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