Display Mean Line Per Group in Facetted Graph Using ggplot2 in R

To display mean per group in facetted graph using ggplot2 in R, we can follow the below steps −

• First of all, create a data frame.

• Then, create the facetted scatterplot between two columns.

• After that, create the facetted scatterplot and add geom_line with mean calculated for y values.

Create the data frame

Let’s create a data frame as shown below −

 Live Demo

x<-sample(1:100,25)
y<-sample(1:100,25)
Group<-sample(c("I","II","III"),25,replace=TRUE)
df<-data.frame(x,y,Group)
df

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

Output

  x   y  Group
1 24 96   II
2 88 81   III
3 22 8    I
4 50 59   II
5 1 33    I
6 56 65   I
7 57 10   II
8 53 54   III
9 54 58   III
10 66 49  III
11 64 50   I
12 23 41   I
13 84 57   I
14 59 14  III
15 96 21   I
16 86 9    I
17 8 71   II
18 85 85  II
19 47 31  II
20 74 63   I
21 25 19  III
22 90 56  II
23 37 1    I
24 82 93   I
25 43 7    I

Create facetted scatterplot

Using facete_grid function of ggplot2 package to create the scatterplot between x and y −

x<-sample(1:100,25)
y<-sample(1:100,25)
Group<-sample(c("I","II","III"),25,replace=TRUE)
df<-data.frame(x,y,Group)
library(ggplot2)
ggplot(df,aes(x,y,col=Group))+geom_point()+facet_grid(~Group)

Output

Display mean line in facetted plot

Using geom_line function and facet_grid function to create the facetted scatterplot between x and y with mean line −

x<-sample(1:100,25)
y<-sample(1:100,25)
Group<-sample(c("I","II","III"),25,replace=TRUE)
df<-data.frame(x,y,Group)
library(ggplot2)
ggplot(df,aes(x,y,col=Group))+geom_point()+facet_grid(~Group)+geom_line(aes(y=mea
n(y)))

Output