Order discrete x scale by frequency value

Question

I am making a dodged bar chart using ggplot with discrete x scale  the x axis are now arranged in alphabetical order  but I need to rearrange it so that it is ordered by the value of the y-axis  i e   the tallest bar will be positioned on the left    I tried order or sort  but result in sort the x-axis  but not the bars respectively   What have I done wrong

User · Accepted Answer

Try manually setting the levels of the factor on the x-axis. For example:

library(ggplot2)
# Automatic levels
ggplot(mtcars, aes(factor(cyl))) + geom_bar()

ggplot of the cars dataset with factor levels automatically determined

# Manual levels
cyl_table <- table(mtcars$cyl)
cyl_levels <- names(cyl_table)[order(cyl_table)]
mtcars$cyl2 <- factor(mtcars$cyl, levels = cyl_levels)
# Just to be clear, the above line is no different than:
# mtcars$cyl2 <- factor(mtcars$cyl, levels = c("6","4","8"))
# You can manually set the levels in whatever order you please. 
ggplot(mtcars, aes(cyl2)) + geom_bar()

ggplot of the cars dataset with factor levels reordered manually

As James pointed out in his answer, reorder is the idiomatic way of reordering factor levels.

mtcars$cyl3 <- with(mtcars, reorder(cyl, cyl, function(x) -length(x)))
ggplot(mtcars, aes(cyl3)) + geom_bar()

ggplot of the cars dataset with factor levels reordered using the reorder function

User · Answer

The best way for me was using vector with categories in order I need as limits parameter to scale x discrete  I think it is pretty simple and straightforward solution   ggplot mtcars  aes factor cyl         geom bar        scale x discrete limits c 8 4 6

User · Answer

You can use reorder   qplot reorder factor cyl  factor cyl  length  data mtcars geom  bar     Edit   To have the tallest bar at the left  you have to use a bit of a kludge   qplot reorder factor cyl  factor cyl  function x  length x  -1      data mtcars geom  bar     I would expect this to also have negative heights  but it doesn t  so it works

User · Answer

I realize this is old  but maybe this function I created is useful to someone out there    order axis lt -function data  axis  column        for interactivity with ggplot2   arguments  lt - as list match call      col  lt - eval arguments column  data    ax  lt - eval arguments axis  data       evaluated factors   a lt -reorder with data  ax                 with data  col       new data   df lt -cbind data frame data      define new var   within df            do call   lt -  list paste0 as character arguments axis    o    a        Now  with this function you can interactively plot with ggplot2  like this    ggplot order axis df  AXIS X  COLUMN Y           aes x   AXIS X o  y   COLUMN Y             geom bar stat    identity     As can be seen  the order axis function creates another dataframe with a new column named the same but with a  oat the end  This new column has levels in ascending order  so ggplot2 automatically plots in that order    This is somewhat limited  only works for character or factor and numeric combinations of columns and in ascending order  but I still find it very useful for plotting on the go

User · Answer

Hadley has been developing a package called forcats  This package makes the task so much easier  You can exploit fct infreq   when you want to change the order of x-axis by the frequency of a factor  In the case of the mtcars example in this post  you want to reorder levels of cyl by the frequency of each level  The level which appears most frequently stays on the left side  All you need is the fct infreq     library ggplot2  library forcats   ggplot mtcars  aes fct infreq factor cyl       geom bar     labs x    cyl     If you wanna go the other way around  you can use fct rev   along with fct infreq     ggplot mtcars  aes fct rev fct infreq factor cyl        geom bar     labs x    cyl

[r] Order discrete x scale by frequency/value

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