Fail to use boxplot in ggplot2

Question

Given such a data frame:

dt       val
02-09     0.1
02-09     0.2
02-09     0.15
02-10     0.3
02-10     -0.1
...

I want to use the boxplot to show the medium, variance of val in each dt:

 ggplot(data = df,aes(y=val,x=dt)) + geom_boxplot()

But what i got is :

It can observed that there is just one box. When I tried outlier.colour = "red", all the points are red. Why? All the values are in the interval of (-1,1)

I see a box for each category. It's hard to see, but apparently you have many identical values (such as 0)? — Roland
– Roland, Commented Feb 25, 2016 at 15:43

Roland · Accepted Answer · 2016-02-25 15:47:23Z

5

This should explain the problem:

set.seed(42)
x <- rnorm(10)
x <- c(x, rep(0, 100)) #add 100 zero values
boxplot(x)

quantile(x, c(0.25, 0.5, 0.75))
#25% 50% 75% 
#  0   0   0

If you have many (almost) identical values, the quartiles are (almost) identical.

answered Feb 25, 2016 at 15:47

Roland

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4 Comments

user5779223 Over a year ago

Solved. I will accept your answer in 3 minutes. Thanks.

user5779223 Over a year ago

Hi, it still regards some of my points as outliers. Do you know how to coverage all the points in the box? Thanks.

Roland Over a year ago

You need to have a look at how a boxplot is defined again. The box covers the quartiles and can't cover all your points.

user5779223 Over a year ago

Sorry , I mean the line of the box, which points to the maximum and minimum value.

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