Filtering을 통한, 새로운 data.frame 생성

[]

airquality[airquality$Month==8 & airquality$Temp>90, ]

with(airquality, airquality[Month==8 & Temp>90, ])

Subset()

subset(airquality,             # data.frame
       select=Ozone:Wind,      # 포함 Column
       select=-c(Temp)         # 제외 Column
       Month==8 & Temp>90)     # Condition

http://stackoverflow.com/questions/9860090/in-r-why-is-better-than-subset

Hadley Wickham 의 글  subset의  위험성  [here].

sqldf()

library(sqldf)
sqldf("SELECT Ozone, Solar.R, Wind 
         FROM airquality
        WHERE Month==8 and Temp>90")

열추가 :: cbind(), trainform()

cbind(airquality, comp=airquality$Temp/airquality$Wind )

with(airquality, cbind(airquality, comp=Temp/Wind ))

transform(airquality, comp=Temp/Wind)

그룹화 :: split()

2nd 인자 기준(grouping factor)으로,  1st 인자를 그룹화시켜  List 생성 

split(airquality$Temp, airquality$Month)  # 월(Month)별 온도(temp)

$`5`
 [1] 67 72 74 62 56 66 65 59 61 69 74 69 66 68 58 64 66 57 68 62 59 73 61 61 57 58 57 67 81 79 76
$`6`
 [1] 78 74 67 84 85 79 82 87 90 87 93 92 82 80 79 77 72 65 73 76 77 76 76 76 75 78 73 80 77 83
$`7`
 [1] 84 85 81 84 83 83 88 92 92 89 82 73 81 91 80 81 82 84 87 85 74 81 82 86 85 82 86 88 86 83 81
$`8`
 [1] 81 81 82 86 85 87 89 90 90 92 86 86 82 80 79 77 79 76 78 78 77 72 75 79 81 86 88 97 94 96 94
$`9`
 [1] 91 92 93 93 87 84 80 78 75 73 81 76 77 71 71 78 67 76 68 82 64 71 81 69 63 70 77 75 76 68