df1 = data.frame(Time = rep(0.5:9.5, each = 10), RoiID = rep(1:10, 10), Diameter = runif(100, 5.0, 7.5),Time.hours=rep(c(1,2)))
I want to extract the legend from the plot and put to another plot by "grid.arrange".
p1=ggplot(data=subset(df1,df1$Time.hours==1), aes(x=factor(RoiID), y=Time, fill = Diameter)) +
theme_minimal() + coord_fixed(ratio=1/2) +
geom_tile(colour = NA, width =1.5 , height = 1)+
scale_fill_gradient(low="black",high="white",limits=c(min(df1$Diameter),max(df1$Diameter)))+
theme(legend.direction="horizontal")
g_legend<-function(a.gplot){
tmp <- ggplot_gtable(ggplot_build(a.gplot))
leg <- which(sapply(tmp$grobs, function(x) x$name) == "guide-box")
legend <- tmp$grobs[[leg]]
return(legend)}
grobs <- ggplotGrob(p1 + theme(legend.position="right"))$grobs
mylegend <- grobs[[which(sapply(grobs, function(x) x$name) == "guide-box")]]
mylegend<-g_legend(p1)
My question is: How to change the title of legend from "Diameter" to " F49 Diameter" (please see image enclosed) before adding the legend to another plot?
If I've understood you correctly, than you just need to add the "F49 Diameter" into scale_fill_gradient
So your code looks like this
p1=ggplot(data=subset(df1,df1$Time.hours==1), aes(x=factor(RoiID), y=Time, fill = Diameter)) +
theme_minimal() + coord_fixed(ratio=1/2) +
geom_tile(colour = NA, width =1.5 , height = 1)+
scale_fill_gradient("F49 Diameter",low="black",high="white",limits=c(min(df1$Diameter),max(df1$Diameter)))+
theme(legend.direction="horizontal")
And than also your extracted legend
library(gridExtra)
grid.arrange(g_legend(p1))
will be named "F49 Diameter"