How do I make a boxplot with two categorical varia

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I would like to make a boxplot that shows how time spent doing a behaviour(Alert) is affected by two variables (Period= Morning/Afternoon and Visitor Level= High/Low).

Alert ~ Period + Vis.Level

'Alert' is a set of 12 numbers that show the amount of time spent awake with the other two as the significant categorical variables. I have looked at other examples but none seem to fit this type of question.

I know the graph I am looking for would have 4 boxplots on it... supposedly with

• PeriodMorning+Vis.LevelHigh
• PeriodMorning+Vis.LevelLow
• PeriodAfternoon+Vis.LevelHigh
• PeriodAfternoon+Vis.LevelLow

on the x axis.

Any help at all would be fantastic!

   Alert Vis.Level    Period
1    0.0       Low   Morning
2    1.0       Low   Morning
3    0.0       Low   Morning
4   11.5       Low Afternoon
5    6.0       Low Afternoon
6   11.5       Low Afternoon
7    0.0      High   Morning
8    0.0      High   Morning
9    0.0      High   Morning
10   0.0      High Afternoon
11   2.5      High Afternoon
12   7.5      High Afternoon

回答1:

Assuming your data looks like this

dd <- structure(list(Alert = c(0, 1, 0, 11.5, 6, 11.5, 0, 0, 0, 0, 
2.5, 7.5), Vis.Level = c("Low", "Low", "Low", "Low", "Low", "Low", 
"High", "High", "High", "High", "High", "High"), Period = c("Morning", 
"Morning", "Morning", "Afternoon", "Afternoon", "Afternoon", 
"Morning", "Morning", "Morning", "Afternoon", "Afternoon", "Afternoon"
)), .Names = c("Alert", "Vis.Level", "Period"), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"))

Then you'll want to make sure your factors are in the correct order

dd$Period<-factor(dd$Period, levels=c("Morning","Afternoon"))
dd$Vis.Level<-factor(dd$Vis.Level, levels=c("Low","High"))

Then you can do

boxplot(Alert~Period+Vis.Level, dd)

or you can get the exact layout you requested with

boxplot(Alert~interaction(Period, Vis.Level, lex.order=T), dd)