R: how to combine ggplots basd on data with different column names-CodePudding

Both ggplots below work separtely, but I would like to combine them to one plot where the Group variable of the lines in df2 appears in the legend.

library(ggplot2)
df1 <- data.frame(x = 1:10, y = 1:10)
df2 <- data.frame(x = rep(1:10,2), 
        y = c(seq(1,2,length.out = 10),
        seq(5,6,length.out = 10)), 
        Group = c(rep("A",10),rep("B",10))          
        )

p1 <- ggplot(data = df1, aes(x = x, y = y))   
geom_point() 

p2<- ggplot(data = df2, aes(x = x, y = y,
group = Group, color = Group))   
geom_line()

The problem is caused by the fact that 2 data frames have different column names. Therefore I cannot generate 2 plots and add them like p1 p2 as it is done in other solutions that have been published here before.

CodePudding user response：

First, in ggplot2 each layer has its own local data argument, i.e. you could pass a different dataset to each layer. If you don't set the data argument for a layer it will simply inherit the global dataset set in ggplot() (if any), i.e. you could combine your plots into one by adding geom_line(data = df2, aes(group = Group, color = Group)) to your first plot.

Second, if your datasets have different column names that's not a big deal either. As with the data argument, each layer has it's own (local) set of aesthetics. If not set, a layer will inherit the global aesthetics set in ggplot(), i.e. with different column names you simply have to tell which columns should be mapped on the aesthetics in each layer.

Slightly altered your example data:

library(ggplot2)
df1 <- data.frame(x1 = 1:10, y1 = 1:10)
df2 <- data.frame(x2 = rep(1:10,2), 
                  y2 = c(seq(1,2,length.out = 10),
                        seq(5,6,length.out = 10)), 
                  Group = c(rep("A",10),rep("B",10))          
)

ggplot(data = df1, aes(x = x1, y = y1))   
  geom_point()  
  geom_line(data = df2, aes(x = x2, y = y2, group = Group, color = Group))