使用ggplot2将2维数据“压缩”到热图中

Question

I have a dataframe like the one below:

obj date    colour  measurement
A   01      red     10
A   02      green   20
A   03      red     5
B   01      green   10
B   02      red     30
B   03      red     50

I know how to present df[,c("obj","date","colour")] in a heatmap format:

chart <- ggplot(data=temp.df,aes(x=date,y=obj,fill=colour))
chart <- chart + geom_tile()

But I want to "squeeze" the "measurement" variable into the plot also, by opacity. That is for A-03, it will be the lightest red, and for B-03, it will be the darkest red.

Is it doable in R and ggplot2? Thanks.

Answer 1

alpha is what you are looking for. Still working on getting a reasonable legend.

 ggplot(df, aes(x=obj,y=date,fill = colour, alpha = measurement)) + 
     geom_tile() + 
     scale_fill_identity() + scale_alpha(guide = 'none')+
     theme_bw() + opts(panel.grid.major = theme_blank())