Sorting boxplots by median in ggplot2

[Nicolay Cunha]

# Dear all,

# I have a question regarding the ordering of boxplots in relation to the

# median in a graph of three factors.

# I want the boxplots getting ordered from the highest to the lowest median

#(stair), within each level of the factor that gives the colors in the

# graphic

# Below the a minimum code

################################################################################################################################

#install.packages("ggplot2")

library(ggplot2)

cmr <- read.table ('http://pastebin.com/raw.php?i=61J9W4Gt', header = T)

str(cmr)

#ordering factors

cmr$height <- factor(cmr$height, levels = c('h','m','l'))

cmr$Pulse <- factor (cmr$Pulse, levels = c("1LF_Low_Short",

"2PF_Low_Short", "2PF_Medium_Medium",

"3GF_Medium_Short","3GF_Medium_Long"))

#plot

ggplot(cmr, aes( height , variable,

colour = factor(pop, levels = pop[order(factor(Pulse))]),

fill = factor(Pulse)))+

xlab ('Anther levels')+

ylab ('Length (mm)')+

scale_colour_manual( values = rep("black", 24), legend = FALSE) +

scale_fill_manual(name = 'Flood Pulse intensity', values =

c("#E5E5E5", "#ACACAC", "#747474", "#3B3B3B", "#030303"))+

geom_boxplot(mapping = NULL, data = NULL, stat = "boxplot", position =

"dodge", outlier.colour = "black",

outlier.shape = 8, outlier.size = 1.5, notch = FALSE, notchwidth =

0.5, show_guide = TRUE)+

theme_bw()

##################################################################

# The question is, how to order the boxplots within each level of Flood

# in descending order of median (several stairways)?

# []

[Greg Snow]

R generally treats information like the ordering of factor levels as a property of the data rather than as a property of the graph.  This means that if you set the order of the factor levels in the factor itself (see the reorder function) then ggplot2 and other plotting and tabling functions will honor that ordering.  Since this should be a property of the data there is generally not an option in the plotting function to change the order.

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[Winston Chang]

You can use reorder() to change the order of factor levels based on another variable. You can modify the original data, or you can put it in line so that ggplot calculates it:

# Original unordered version

ggplot(InsectSprays, aes(x = spray, y = count)) + geom_boxplot()

# Ordered by median

ggplot(InsectSprays, aes(x = reorder(spray, count, FUN=median), y = count)) + geom_boxplot()

-Winston

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