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I am trying to change x axis tick labels of a box-plot generated by ggplot2. The x axis is a categorical variable (HabFac), what I want is to change its ticks to 6 Chemicals (A-E). Below is my code:

raw_data=read.table(##Read data##) p_TT=ggplot(raw_data, aes(x= HabFac , y = logTissueConc, fill = Chemical)) + geom_boxplot() ###find out x axis breaks dd_TT=ggplot_build(p_TT) dd_TT$data[[1]]$x ##Modify the x ticks p_TT=p_TT+ scale_x_discrete(breaks=dd_TT$data[[1]]$x, labels = letters[1:7])

However, my code does not work.... Can anyone give me some suggestions?

 Species Chemical logTissueConc HabFac 1 Barking treefrog A -1.10922426 Arboreal 2 Barking treefrog A -1.55698525 Arboreal 3 Barking treefrog A -0.67977088 Arboreal 4 Barking treefrog A -1.22868756 Arboreal 5 Barking treefrog A -0.47476868 Arboreal 6 Barking treefrog B -0.89399639 Arboreal 7 Barking treefrog B -1.35670286 Arboreal 8 Barking treefrog B -2.35421158 Arboreal 9 Barking treefrog B -2.49491771 Arboreal 10 Barking treefrog B -2.30921816 Arboreal 11 Barking treefrog C 2.06394108 Arboreal 12 Barking treefrog C 1.84732292 Arboreal 13 Barking treefrog C 1.62127641 Arboreal 14 Barking treefrog C 1.72991810 Arboreal 15 Barking treefrog C 1.72845824 Arboreal 16 Barking treefrog C -0.42136482 Arboreal 17 Barking treefrog C -0.03384518 Arboreal 18 Barking treefrog C -0.76756916 Arboreal 19 Barking treefrog C -0.77322993 Arboreal 20 Barking treefrog C -1.20469607 Arboreal 21 Barking treefrog D -1.31449937 Arboreal 22 Barking treefrog D -1.52823116 Arboreal 23 Barking treefrog D -1.94002471 Arboreal 24 Barking treefrog D -1.29272381 Arboreal 25 Barking treefrog D -1.75399776 Arboreal 26 Cricket frog A -1.37352233 Aquatic 27 Cricket frog A -0.83291030 Aquatic 28 Cricket frog A -0.98828589 Aquatic 29 Cricket frog A -1.08040579 Aquatic 30 Cricket frog A -1.28747727 Aquatic 31 Cricket frog E 0.73098756 Aquatic 32 Cricket frog E 0.56309363 Aquatic 33 Cricket frog E 0.55666185 Aquatic 34 Cricket frog E 0.37853050 Aquatic 35 Cricket frog E 0.31730552 Aquatic
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You need to provide a function to the labels argument that maps the existing labels to new ones. Consider the following:

qplot(Species,Petal.Length,data=iris)+scale_x_discrete(labels=toupper)

To answer your question more directly, you would need to construct a function that maps the existing label from the data to a position in a vector of your new labels. If your existing data is a factor you could use something like:

qplot(Species,Petal.Length,data=iris)+scale_x_discrete(labels=function(x) letters[1:3][which(x==levels(iris$Species))])
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Thanks for the suggestion. This is like re-mapping, right? May I know how to increase the number of tick labels? Previously, I have two, but I need seven now..

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