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I have this data frame y. I am trying to create a heatmap using ggplot. I would like to reverse the order of y-axis. The top value should be 00:00 and the values should be decrementing to 23:59. For example, the top value should be 00:00, then 01:00, 02:00, 03:00, etc. Rigth now, y-axis is going up from 01:00, then 02:00, 03:00 etc. Any ideas how I can do this in ggplot2?

 cols<-c("white","#F0FFFF","#BBFFFF","#00FFFF","#42C0FB","#1C86EE", "green","yellow","#C9821E", "#FF0000", "#FF0000") vals<-c(0,0.19,0.29,0.39, 0.49,0.59, 0.69, 0.79, 0.89, 0.90,1) brk<-c(20, 30, 40, 50, 60, 70, 80, 90, 100) ggplot(y,aes(DATE, Time, fill=CPU)) + geom_tile() + theme_bw() + scale_fill_gradientn(name="CPU Utilization", colours=cols, values=val, limits=c(0,100), breaks = brk) + guides(fill = guide_legend(keywidth = 5, keyheight = 1))+ scale_x_date(breaks = "1 days", labels=date_format("%a")) + coord_trans(y="reverse")

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 dput(head(y,50)) structure(list(DATE = structure(c(15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809), class = "Date"), Time = c("20:14", "20:29", "20:44", "20:59", "21:14", "21:29", "21:44", "21:59", "22:14", "22:29", "22:44", "22:59", "23:14", "23:29", "23:44", "23:59", "00:14", "00:29", "00:44", "00:59", "01:14", "01:29", "01:44", "01:59", "02:14", "02:29", "02:44", "02:59", "03:14", "03:29", "03:44", "03:59", "04:14", "04:29", "04:44", "04:59", "05:14", "05:29", "05:44", "05:59", "06:14", "06:29", "06:44", "06:59", "07:14", "07:29", "07:44", "07:59", "08:14", "08:29"), CPU = c(30, 30, 30, 31, 30, 27, 25, 23, 24, 22, 20, 21, 22, 21, 20, 20, 20, 15, 17, 15, 20, 16, 15, 16, 15, 14, 14, 11, 12, 11, 19, 22, 22, 21, 19, 20, 20, 17, 16, 10, 9, 9, 9, 10, 12, 13, 14, 14, 16, 16)), .Names = c("DATE", "Time", "CPU"), row.names = 4205:4254, class = "data.frame")
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  • anybody? I cannot seem to find a solution on this. Commented Apr 25, 2013 at 20:29
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    First off, I can't currently run your code because (at least) some objects are missing (brk, cols, val). Second, y$Time gets silently converted to factor with levels in alphabetical order. Try converting it before plotting: y$Time = factor(y$Time, levels=sort(unique(y$Time), decreasing=TRUE)). Commented Apr 26, 2013 at 0:12
  • @bdemarest, I am sorry, I've updated the original post with those values. The reason I have time as POSIXct is that I can use scale_y_datetime function to only show %H and %M. Commented Apr 26, 2013 at 13:04
  • @bdemarest, this looks like this going to be workinb but I have one little problem. I need to scale my y-axis so that not all of the values show up, show time values for every 2 hours to make the y-axis more readable, any ideas? Commented Apr 26, 2013 at 13:26

1 Answer 1

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Since ggplot2 converts your y-axis values to a factor, just convert all values to the factor of interest in advance:

library(ggplot2) y <- data.frame(DATE = structure(c(15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809, 15809), class = "Date"), Time = c("20:14", "20:29", "20:44", "20:59", "21:14", "21:29", "21:44", "21:59", "22:14", "22:29", "22:44", "22:59", "23:14", "23:29", "23:44", "23:59", "00:14", "00:29", "00:44", "00:59", "01:14", "01:29", "01:44", "01:59", "02:14", "02:29", "02:44", "02:59", "03:14", "03:29", "03:44", "03:59", "04:14", "04:29", "04:44", "04:59", "05:14", "05:29", "05:44", "05:59", "06:14", "06:29", "06:44", "06:59", "07:14", "07:29", "07:44", "07:59", "08:14", "08:29"), CPU = c(30, 30, 30, 31, 30, 27, 25, 23, 24, 22, 20, 21, 22, 21, 20, 20, 20, 15, 17, 15, 20, 16, 15, 16, 15, 14, 14, 11, 12, 11, 19, 22, 22, 21, 19, 20, 20, 17, 16, 10, 9, 9, 9, 10, 12, 13, 14, 14, 16, 16)) y$Time <- factor(y$Time, levels=rev(sort(y$Time))) cols<-c("white","#F0FFFF","#BBFFFF","#00FFFF","#42C0FB","#1C86EE", "green","yellow","#C9821E", "#FF0000", "#FF0000") vals<-c(0,0.19,0.29,0.39, 0.49,0.59, 0.69, 0.79, 0.89, 0.90,1) brk<-c(20, 30, 40, 50, 60, 70, 80, 90, 100) ggplot(y,aes(DATE, Time, fill=CPU)) + geom_tile() + theme_bw() + scale_fill_gradientn(name="CPU Utilization", colours=cols, values=vals, limits=c(0,100), breaks = brk)

plot as shown

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