#data.frames

> DATA FRAMES

(if you only have 1 var in the data frame, treated like a list--with 2 or more vectors, df behaves like matrix)

Taken directly from site:  How many of your friends complain regularly about their bodies? ~None: 147 ~A few: 411 ~Some: 188 ~Most: 141 ~All: 53

construct an object that reflects it:

> body_complain<-data.frame(x=c('None','A few','Some','Most','All'),y=c(147,411,188,141,53))

object $ title of column

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>DATA FRAMES>STRUCTURAL QUALITIES

the structure of data frame subsets are unique 

examine the differences using this variable (a)

> a  x y z 1 1 1 a 2 2 2 b 3 3 3 c 4 4 4 d

> str(a) 'data.frame':   4 obs. of  3 variables: $ x: int  1 2 3 4 $ y: int  1 2 3 4 $ z: Factor w/ 4 levels "a","b","c","d": 1 2 3 4

Now examine the structural differences which subsetting initiates in data frames

> str(a[c(1)]) 'data.frame':   4 obs. of  1 variable: $ x: int  1 2 3 4

> str(a[,c(1,3)]) 'data.frame':   4 obs. of  2 variables: $ x: int  1 2 3 4 $ z: Factor w/ 4 levels "a","b","c","d": 1 2 3 4

> str(a[c(3),]) 'data.frame':   1 obs. of  3 variables: $ x: int 3 $ y: int 3 $ z: Factor w/ 4 levels "a","b","c","d": 3

To access a subscript of a data frame use $ and []

>a$y[3]

[1] 3

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>DATA FRAME > REASSIGNMENT