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3. 散點圖
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散點圖通常用于刻畫兩個連續型變量之間的關系。繪制散點圖時，數據集中的每一個觀測值都由每個點表示。
3.1 繪制基本散點圖
library(gcookbook)
library(ggplot2)
# 列出我們用到的列
head(heightweight[, c("ageYear", "heightIn")])
> head(heightweight[, c("ageYear", "heightIn")])
ageYear heightIn
1 11.92 56.3
2 12.92 62.3
3 12.75 63.3
4 13.42 59.0
5 15.92 62.5
6 14.25 62.5
ggplot(heightweight, aes(x=ageYear, y=heightIn)) + geom_point()
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# shape參數設置點型 size設置點的大小
ggplot(heightweight, aes(x=ageYear, y=heightIn)) +
geom_point(shape=21)
ggplot(heightweight, aes(x=ageYear, y=heightIn)) +
geom_point(size=1.5)
image-20210816225649979
3.2 使用點形和顏色屬性進行分組
head(heightweight[, c("sex", "ageYear", "heightIn")])
> head(heightweight[, c("sex", "ageYear", "heightIn")])
sex ageYear heightIn
1 f 11.92 56.3
2 f 12.92 62.3
3 f 12.75 63.3
4 f 13.42 59.0
5 f 15.92 62.5
6 f 14.25 62.5
ggplot(heightweight, aes(x=ageYear, y=heightIn, colour=sex)) +
geom_point()
ggplot(heightweight, aes(x=ageYear, y=heightIn, shape=sex)) +
geom_point()
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# scale_shape_manual()使用其它點形狀
#scale_colour_brewer()使用其它顏色
ggplot(heightweight, aes(x=ageYear, y=heightIn, shape=sex, colour=sex)) +
geom_point() +
scale_shape_manual(values=c(1,2)) +
scale_colour_brewer(palette="Set1")
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3.3 使用不同于默認設置的點形
# 使用點形和填充色屬性分別表示不同變量
hw <- heightweight
# 分組 Categorize into <100 and >=100 groups
hw$weightGroup <- cut(hw$weightLb, breaks=c(-Inf, 100, Inf),
labels=c("< 100", ">= 100"))
# 使用具有顏色和填充色的點形及對應于空值(NA)和填充色的顏色
ggplot(hw, aes(x=ageYear, y=heightIn, shape=sex, fill=weightGroup)) +
geom_point(size=2.5) +
scale_shape_manual(values=c(21, 24)) +
scale_fill_manual(values=c(NA, "black"),
guide=guide_legend(override.aes=list(shape=21)))
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3.4 將連續型變量映射到點的顏色或大小屬性上
ggplot(heightweight, aes(x=ageYear, y=heightIn, colour=weightLb)) +
geom_point()
ggplot(heightweight, aes(x=ageYear, y=heightIn, size=weightLb)) +
geom_point()
image-20210817114855294
# 默認點的大小范圍為1-6mm
# scale_size_continuous(range=c(2, 5))修改點的大小范圍
# 將色階設定為由黑至白
ggplot(heightweight, aes(x=weightLb, y=heightIn, fill=ageYear)) +
geom_point(shape=21, size=2.5) +
scale_fill_gradient(low="black", high="white")
# 使用 guide_legend() 函數以離散的圖例代替色階
ggplot(heightweight, aes(x=weightLb, y=heightIn, fill=ageYear)) +
geom_point(shape=21, size=2.5) +
scale_fill_gradient(low="black", high="white", breaks=12:17,
guide=guide_legend())
image-20210817165620820
# 調用scale_size_area()函數使數據點的面積正比于變量值。
ggplot(heightweight, aes(x=ageYear, y=heightIn, size=weightLb, colour=sex)) +
geom_point(alpha=.5) +
scale_size_area() +
scale_colour_brewer(palette="Set1")
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3.5 處理圖形重疊
方法：
- 使用半透明的點
- 將數據分箱(bin)，并用矩形表示
- 將數據分箱(bin)，并用六邊形表示
- 使用箱線圖
sp <- ggplot(diamonds, aes(x=carat, y=price))
sp + geom_point()
# 透明度
sp + geom_point(alpha=.1)
sp + geom_point(alpha=.01)
# stat_bin2d()函數默認分別在x軸和y軸方向上將數據分割為30各組
sp + stat_bin2d()
# bin=50設置箱數,limits參數設定圖例范圍
sp + stat_bin2d(bins=50) +
scale_fill_gradient(low="lightblue", high="red", limits=c(0, 6000))
image-20210817173245460
# stat_binhex()函數使用六邊形分箱
library(hexbin)
sp + stat_binhex() +
scale_fill_gradient(low="lightblue", high="red",
limits=c(0, 8000))
sp + stat_binhex() +
scale_fill_gradient(low="lightblue", high="red",
breaks=c(0, 250, 500, 1000, 2000, 4000, 6000),
limits=c(0, 6000))
image-20210817174431437
sp1 <- ggplot(ChickWeight, aes(x=Time, y=weight))
sp1 + geom_point()
# 調用position_jitter()函數給數據點增加隨機擾動,通過width,height參數調節
sp1 + geom_point(position="jitter")
# 也可以調用 geom_jitter()
sp1 + geom_point(position=position_jitter(width=.5, height=0))
image-20210817175225507
# 箱線圖
sp1 + geom_boxplot(aes(group=Time))
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參考書籍
- R Graphics Cookbook, 2nd edition.
