ベイズ統計モデリング 写経2

3.4.1.5 ベクトルへのアクセス

x=c(2.718, 3.14, 1.414, 47405)

names(x)=c("e","pi","sqrt2","zipcode")

どの要素を返すか数値で指定

x[c(2,4)]

##       pi  zipcode 
##     3.14 47405.00

どの要素を除外するか指定

x[c(-1,-3)]

##       pi  zipcode 
##     3.14 47405.00

それぞれの要素を返すか指定する

x[c(FALSE,TRUE,FALSE,TRUE)]

##       pi  zipcode 
##     3.14 47405.00

要素名を指定する

x[c("pi","zipcode")]

##       pi  zipcode 
##     3.14 47405.00

3.4.2 ファクター型

x=c("high","medium","low", "high","medium")

ファクター型に変換

xf=factor(x)
xf

## [1] high   medium low    high   medium
## Levels: high low medium

factor型を数値に変換

as.numeric(xf)

## [1] 1 3 2 1 3

levelsを指定

xfo=factor(x, levels=c("low","medium","high"), ordered=TRUE)
xfo

## [1] high   medium low    high   medium
## Levels: low < medium < high

as.numeric(xfo)

## [1] 3 2 1 3 2

既に存在しているfactor型のlevelを変更

x=c("high","medium","low", "high","medium")
xf=factor(x)
xf

## [1] high   medium low    high   medium
## Levels: high low medium

as.numeric(xf)

## [1] 1 3 2 1 3

xf=factor(xf, levels=c("low","medium","high"), ordered=TRUE)
xf

## [1] high   medium low    high   medium
## Levels: low < medium < high

as.numeric(xf)

## [1] 3 2 1 3 2

levelsの名前を変えたい場合

xfol=factor(xf, levels=c("low","medium","high"), ordered=TRUE, labels = c("bottom", "middle", "top"))
xfol

## [1] top    middle bottom top    middle
## Levels: bottom < middle < top