处理data.frames

Question

I have a sample survey sheet; something like demographic. One of the columns is country (factor) another is annual income . Now, I need to calculate average of each country and store in new data.frame with country and corresponding mean . It should be simple but I am lost. The data is something like the one shown below:

Country  Income($) Education ... ... ...
1. USA    90000      Phd
2. UK     94000      Undergrad
3. USA    94000      Highschool
4. UK     87000      Phd
5. Russia 77000      Undergrad
6. Norway 60000      Masters
7. Korea  90000      Phd
8. USA    110000     Masters
.
.

I need a final result like:

USA   UK    Russia ...
98000 90000 75000

Thank You.

Answer 1

data example:

dat <- read.table(text="Country  Income Education 
 USA    90000      Phd
 UK     94000      Undergrad
 USA    94000      Highschool
 UK     87000      Phd
 Russia 77000      Undergrad
 Norway 60000      Masters
 Korea  90000      Phd
 USA    110000     Masters",header=TRUE)

Do what you want with plyr :

if your data is called dat :

library(plyr)
newdf <- ddply(dat, .(Country), function(x) Countrymean = mean(x$Income))

# newdf <- ddply(dat, .(Country), function(x) data.frame(Income = mean(x$Income)))

and aggregate:

 newdf <- aggregate(Income ~ Country, data = dat, FUN = mean)

for the output you show at the end maybe tapply ?

tapply(dat$Income, dat$Country, mean)