12.2. GGPlot2

The grammar of graphics has following ideas:

• data set
• coordinate systems
• scales
• geometrical objects (points, lines, boxes, bars, etc.)
• aesthetics (size, color, transparency, etc.)
• facets

List of aesthetics

Aesthetic	Description	Details
color	color of points
size	size of points
shape	shape of points	6 shapes by default
fill	fill color for bars, etc.
alpha	transparency	0 - totally transparent, 1 - totally opaque
stroke
linetype

We will prepare a data set consisting of points from three noisy lines:

> x <- c(1:10)
> y1 <- 4 * x + 2*rnorm(10)
> y2 <- 3.5 * x + 2*rnorm(10)
> y3 <- 2 * x + 2*rnorm(10)
> y <- c(y1, y2, y3)
> x <- rep(x, 3)
> index <- rep(1:3, each=10)
> df <- data.frame(index=index, x=x, y=y)
> df
   index  x         y
1      1  1  4.970771
2      1  2  8.178185
3      1  3 10.698853
4      1  4 13.931963
5      1  5 20.264946
6      1  6 22.301773
7      1  7 28.370019
8      1  8 32.313593
9      1  9 37.628974
10     1 10 42.292327
11     2  1  3.052891
12     2  2  2.792227
13     2  3 12.092148
14     2  4 16.325021
15     2  5 18.509915
16     2  6 17.871619
17     2  7 24.220242
18     2  8 30.617569
19     2  9 31.180454
20     2 10 33.617135
21     3  1  2.024496
22     3  2  1.985061
23     3  3  6.995560
24     3  4  6.292036
25     3  5  7.542600
26     3  6  9.227137
27     3  7 15.913043
28     3  8 15.263772
29     3  9 19.253074
30     3 10 20.927419

> qplot(x, y, data=df)

Plotting data from line 1 as a line:

> df[df$index==1, ]
   index  x         y
1      1  1  4.970771
2      1  2  8.178185
3      1  3 10.698853
4      1  4 13.931963
5      1  5 20.264946
6      1  6 22.301773
7      1  7 28.370019
8      1  8 32.313593
9      1  9 37.628974
> qplot(x, y, data=df[df$index == 1, ], geom='line')

> qplot(mpg, hp, data=mtcars)

> qplot(mpg, wt, data=mtcars)

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