r - 如何在R中叠加散点图？

Question

如果我有三组数据：

a1= rnorm(10)
a2= rnorm(10)
a3= rnorm(10)

而不是使用以下方法并排查看这些：

par(mfrow=c(1,3))
plot(a1)
plot(a2)
plot(a3)

我如何在同一个情节上获得所有这些点？

Answer 1

只需使用以下points功能：

plot(a1)
points(a2, col=2)
points(a3, col=3)

这相当于：

plot(1:length(a1), a1)
points(1:length(a2), a2, col=2)
points(1:length(a3), a3, col=3)

如果向量的长度不等，则应指定 x 轴限制：

plot(a1, xlim=c(1, max(length(a1), length(a2), length(a3))))

Answer 2

# To overlay scatterplots in R

# import the required libraries
library(ggplot2)
library(reshape2)

# assign data
a1=rnorm(10)
a2=rnorm(10)
a3=rnorm(10)

# create a dataframe from combined data
# and set count to however many points are in each dataset
df = data.frame(a1, a2, a3, count = c(1:10))

# melt the dataframe
df.m = melt(df, id.vars ="count", measure.vars = c("a1","a2","a3"))

# take a look at what melt() does to get an idea of what is going on
df.m

# plot out the melted dataframe using ggplot
ggplot(df.m, aes(count, value, colour = variable)) + geom_point() + ylim(-3,3)

# swapping the axis
ggplot(df.m, aes(value, count, colour = variable)) + geom_point() + xlim(-3,3)

当a1和a3大小相等时，无法放入与列相同data.frame的列中，作为 的输入melt。解决方案是简单地使用list：

a1 = rnorm(10)
a2 = rnorm(25)
a3 = rnorm(17)
a_list = list(a1, a2, a3)
a_df = do.call("rbind", lapply(a_list, 
                                function(x) data.frame(value = x, 
                                                       count = seq_along(x))))
ID_options = LETTERS[seq_along(a_list)]
a_df$ID = rep(ID_options, sapply(a_list, length))
ggplot(a_df, aes(x = value, y = count, color = ID)) + geom_point()

Answer 3

要增加答案的多样性，您还可以使用lattice. 在这里，每组代码示例中的第二行代表交换的轴。

library(lattice)

## If you have already created the "df" 
##   data.frame from your example
xyplot(count ~ a1 + a2 + a3, data=df)
xyplot(a1 + a2 + a3 ~ count, data=df)

## Without first creating the "df" 
##   data.frame from your example    
xyplot(1:10 ~ a1 + a2 + a3)
xyplot(a1 + a2 + a3 ~ 1:10)

如果您正在使用不等长的向量，您可以从我分享的关于不等长向量的答案cbind中加载函数，然后使用我提到的第一种方法。更新：有关该功能的最新版本，请参阅https://gist.github.com/mrdwab/6789277 。

例子：

a1 = rnorm(10)
a2 = rnorm(25)
a3 = rnorm(17)

library(lattice)
library(devtools)
## source_gist is not working properly unless you provide 
##   the full URL to the "raw" file
source_gist("https://gist.github.com/mrdwab/6789277/raw/9bd7d5931389ec475c49c1918d26d9899796a5d0/Cbind.R")

newdf <- Cbind(a1, a2, a3)
xyplot(a1 + a2 + a3 ~ sequence(nrow(newdf)), data=newdf)
xyplot(sequence(nrow(newdf)) ~ a1 + a2 + a3, data=newdf)

这是一个示例图，对默认颜色进行了一些调整：

xyplot(sequence(nrow(newdf)) ~ a1 + a2 + a3, data=newdf, 
       pch = 21, fill = c("black", "red", "green"), cex = 1)