nclass Exercise4_20211013

Regarding UCBAdmissions{datasets} data object, what does the output (1)UCBAdmissions[,1,] (2)UCBAdmissions[,1,1] (3)UCBAdmissions[1,1,]

UCBAdmissions{datasets}

data(birthwt, package = "MASS")
dta<-UCBAdmissions
str(dta)

##  'table' num [1:2, 1:2, 1:6] 512 313 89 19 353 207 17 8 120 205 ...
##  - attr(*, "dimnames")=List of 3
##   ..$ Admit : chr [1:2] "Admitted" "Rejected"
##   ..$ Gender: chr [1:2] "Male" "Female"
##   ..$ Dept  : chr [1:6] "A" "B" "C" "D" ...

dim(dta)

## [1] 2 2 6

class(dta)

## [1] "table"

typeof(dta)

## [1] "double"

head(dta)

## , , Dept = A
## 
##           Gender
## Admit      Male Female
##   Admitted  512     89
##   Rejected  313     19
## 
## , , Dept = B
## 
##           Gender
## Admit      Male Female
##   Admitted  353     17
##   Rejected  207      8
## 
## , , Dept = C
## 
##           Gender
## Admit      Male Female
##   Admitted  120    202
##   Rejected  205    391
## 
## , , Dept = D
## 
##           Gender
## Admit      Male Female
##   Admitted  138    131
##   Rejected  279    244
## 
## , , Dept = E
## 
##           Gender
## Admit      Male Female
##   Admitted   53     94
##   Rejected  138    299
## 
## , , Dept = F
## 
##           Gender
## Admit      Male Female
##   Admitted   22     24
##   Rejected  351    317

結論： 1.UCBAdmissions資料型態是array，2x2x6的table 2.$Admit : chr [1:2] “Admitted” “Rejected” $Gender: chr [1:2] “Male” “Female” $Dept : chr [1:6] “A” “B” “C” “D” …

UCBAdmissions[?,?,?]

dta[0,,]

## < table of extent 0 x 2 x 6 >

dta[1,,]

##         Dept
## Gender     A   B   C   D   E   F
##   Male   512 353 120 138  53  22
##   Female  89  17 202 131  94  24

dta[2,,]

##         Dept
## Gender     A   B   C   D   E   F
##   Male   313 207 205 279 138 351
##   Female  19   8 391 244 299 317

結論： 因為不懂UCBAdmissions[?,?,?]各?代表的意思，因此試試看。 1.沒有0x2x6的資料 2.UCBAdmissions[1,?,?] Admit(Admitted) x Gender x Dept 3.UCBAdmissions[2,?,?] Admit(Rejected) x Gender x Dept

#UCBAdmissions[,1,]

dta[,1,]   #Admit x Gender(1=Male) x Dept

##           Dept
## Admit        A   B   C   D   E   F
##   Admitted 512 353 120 138  53  22
##   Rejected 313 207 205 279 138 351

結論： UCBAdmissions[,1,] 提取Gender為男性的，做Admit x Dept的table為2x6

UCBAdmissions[,1,1]

dta[,1,1]   #Admit x Gender(1=Male) x Dept(1=A)

## Admitted Rejected 
##      512      313

結論： UCBAdmissions[,1,1] 提取Gender為男性且Dept為A的，做出來的table只剩下2x1(Admitted或Rejected)

UCBAdmissions[1,1,]

dta[1,1,]  #Admit(1=Admitted) x Gender(1=Male) x Dept

##   A   B   C   D   E   F 
## 512 353 120 138  53  22

結論： UCBAdmissions[1,1,] 提取Admit為Admitted且Gender為Male的，做出來的table只剩下1x6(Dept A~F)

殘存問題

1.為何typeof(UCBAdmissions)是double?