I am looking for how to make a box plot with the base function boxplot() in R for two animal groups and two sex groups. I need four boxes for female sheep, male sheep, female goats, and male goats to show the difference in animal height.
animal sex height
1 sheep female 117
2 sheep female 115
3 sheep female 110
4 sheep male 95
5 sheep male 121
6 sheep male 106
7 sheep female 98
8 sheep female 119
9 sheep female 100
10 sheep male 121
11 goat male 130
12 goat male 125
13 goat male 134
14 goat female 112
15 goat female 122
16 goat female 129
17 goat male 135
18 goat male 139
With this code I have only two boxes for sheep and goats:
boxplot (height ~ animal)
I haven't tried it on your data, but the last example in ?boxplot shows the use of an interaction: something like
boxplot (height ~ animal:sex, data = your_data)
should do it (see the examples for more details on specifying fill colours and other decorations).
(@GregorThomas suggests + instead of :, and the help for the "formula" argument says
Note that ‘~ g1 + g2’ is equivalent to ‘g1:g2’.
)