R - 将 ggplot2 与两个不同大小的数据集一起使用

Question

I want to do a scatter plot for two datasets with different sizes.

Imagine I have two data.frames: df1, df2. The row size of df1 is 100, and of df2 is 50. Is there a way to do a scatter plot with ggplot2? I've searched but couldn't find anything. The online tutorials always assume that the datasets are of the same size, with equal value for the x-axis. Also, I want to plot the two datasets in the same graph, not side-by-side.

Here's some exemplifying data:

df1<-data.frame(X1=1:10,Y11=11:20,Y12=21:30,Y13=31:40)

df2<-data.frame(X2=1.5:10.5,Y21=1.5:10.5)

Let's imagine X1 is a column with values measuring distance in km. Y11 is the vector with values for fuel consumption for Car1, Y12 is the vector with values for fuel consumption for Car2, and so on. Now X2 is still vector with values measuring distance in km, different from X1, but in the same range. Y21 is the fuel consumption for a modified Car1. I want to put them in the same scatter plot, with x-axis being distance(km) and y-axis being fuel consumption

Answer 1

This would be much easier to answer if you gave an example data set. but here is what you can do (make sure each data.frame has the same column names):

df1 <- data.frame(x = 1:50, y = 1:50)
df2 <- data.frame(x = 100:1, y = 1:100)

df1$cat <- "df1"
df2$cat <- "df2"

df <- rbind(df1, df2)

library(ggplot2)
ggplot(df, aes(x, y, color = cat))+
  geom_point()

and that gives you this:

Answer 2

If you want to plot all the data together, then It's best to reshape your data. Here's an example using other tidyverse functions

library(tidyr)
library(dplyr)

dd <- bind_rows(
  df1 %>% gather(car, mpg, -X1) %>% rename(X=X1),
  df2 %>% gather(car, mpg, -X2) %>% rename(X=X2)
)

ggplot(dd, aes(X, mpg, color=car)) + geom_point()

Answer 3

It's an old question, but recently I have solved a similar problem using a quicker approach than the ones here

ggplot with 2 y axes on each side and different scales

Maybe you can first scale down one of the datasets, and then try out the "dual y-axes" function in ggplot2, namely,

p <– ggplot2(dataframe, ...)+...
p + scale_y_continuous(name, ..., sec.axis = sec_axis(...))

where sec.axis means "the second axis" Please refer to https://www.r-graph-gallery.com/line-chart-dual-Y-axis-ggplot2.html for details. ?sec_axis in R also helps.

Answer 4

Thanks to a comment by MrFrick, I think I got it.

ggplot(data=df1) + geom_point(aes(x=X1,y=Y11, 
                          color="Car1"))+
  geom_point(data=df2,aes(x=X2,y=Y21),color="ModCar2"))