How to find the mean of a continuous variable for each categorical variable

Question

I\'d like to plot continuous BMI on the y-axis and the categorical variable for Family Income on the x-axis and I\'d like the graph to plot the mean BMI for each category. Howev

Answer 1

This may work:

    library(plyr)
    nhh<-ddply(nh,.(famIncome), summarise, mean.bmi=mean(bmi)) # find mean bmi
    with(nhh, plot(famIncome,mean.bmi)) # simple plot

Answer 2

Here's a base solution using aggregate:

a <- aggregate(BMI ~ FamIncome, data=nh, FUN=mean)
barplot(a$BMI, names.arg=a$FamIncome)