change x location of violin plot in ggplot2

I was trying to create a violin plot using a continuous variable factored in x. I currently have the x values of 0,3,5,8. When I plot them as a violin they show up equally spaced from each other. Is there a way to force the locations of the violins to be at essentially 0,3,5,8?

I included some sample data and the line I was essentially trying to run.

condition movedur
[1,] 5 0.935
[2,] 0 1.635
[3,] 3 0.905
[4,] 8 0.875
[5,] 3 1.060
[6,] 8 1.110
[7,] 3 1.830
[8,] 5 1.060
[9,] 5 1.385
[10,] 5 1.560
[11,] 0 1.335
[12,] 3 0.880
[13,] 0 1.030
[14,] 8 1.300
[15,] 3 1.230
[16,] 3 1.210
[17,] 5 1.710
[18,] 3 1.000
[19,] 0 1.365
[20,] 0 1.000

ggplot(a, aes(x = condition, y = movedur, fill = condition)) +
geom_violin()


When I run the full code I get the image below. But the x axis is equally spaced instead of being spaced by the values.

2 Answers
2

If you leave the condition variable as an integer/numeric for the x axis but use it as a factor for fill you can get the plot you want.

condition

fill

Note that the dataset example you give already has condition as an integer, but if it is a factor and you want to convert it you could do

condition

a$condition = as.numeric(as.character(a$condition))

a$condition = as.numeric(as.character(a$condition))

I add breaks in scale_x_continuous() to make the breaks look nice.

breaks

scale_x_continuous()

ggplot(a, aes(x = condition, y = movedur, fill = factor(condition))) +
geom_violin() +
scale_x_continuous(breaks = c(0, 3, 5, 8) )


This is because violin plots are intended to be used for categorical data on the x-axis and so it is just treating the different values of condition as categories rather than values on a continuous axis. To get the desired result you can insert missing values corresponding to the other axis values with complete as shown below. Note that you need to insert a factor call to get ggplot2 to use a discrete fill scale.

condition

complete

factor

ggplot2

fill

library(tidyverse)
tbl <- structure(list(condition = c(5L, 0L, 3L, 8L, 3L, 8L, 3L, 5L, 5L, 5L, 0L, 3L, 0L, 8L, 3L, 3L, 5L, 3L, 0L, 0L), movedur = c(0.935, 1.635, 0.905, 0.875, 1.06, 1.11, 1.83, 1.06, 1.385, 1.56, 1.335, 0.88, 1.03, 1.3, 1.23, 1.21, 1.71, 1, 1.365, 1)), row.names = c(NA, -20L), class = c("tbl_df", "tbl", "data.frame"), spec = structure(list(cols = list(condition = structure(list(), class = c("collector_integer", "collector")), movedur = structure(list(), class = c("collector_double", "collector"))), default = structure(list(), class = c("collector_guess", "collector"))), class = "col_spec"))

tbl %>%
complete(condition = 0:8) %>%
ggplot() +
geom_violin(aes(x = condition, y = movedur, fill = factor(condition)))
#> Warning: Removed 5 rows containing non-finite values (stat_ydensity).


Created on 2018-07-02 by the reprex package (v0.2.0).

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