since the data ex1221new was not given, so I have created a dummy data and added it to a data frame. Also, the question which was asked has few changes in codes like then ggplot package has deprecated the use of
"scale_area()" and nows uses scale_size_area()
"opts()" has changed to theme()
In my answer,I have stored the plot in mygraph variable and then I have used
mygraph$labels$x="Discharge of materials" #changes x axis title
mygraph$labels$y="Area Affected" # changes y axis title
And the work is done. Below is the complete answer.
install.packages("Sleuth2")
library(Sleuth2)
library(ggplot2)
ex1221new<-data.frame(Discharge<-c(100:109),Area<-c(120:129),NO3<-seq(2,5,length.out = 10))
discharge<-ex1221new$Discharge
area<-ex1221new$Area
nitrogen<-ex1221new$NO3
p <- ggplot(ex1221new, aes(discharge, area), main="Point")
mygraph<-p + geom_point(aes(size= nitrogen)) +
scale_size_area() + ggtitle("Weighted Scatterplot of Watershed Area vs. Discharge and Nitrogen Levels (PPM)")+
theme(
plot.title = element_text(color="Blue", size=30, hjust = 0.5),
# change the styling of both the axis simultaneously from this-
axis.title = element_text(color = "Green", size = 20, family="Courier",)
# you can change the axis title from the code below
mygraph$labels$x="Discharge of materials" #changes x axis title
mygraph$labels$y="Area Affected" # changes y axis title
mygraph
Also, you can change the labels title from the same formula used above -
mygraph$labels$size= "N2" #size contains the nitrogen level