[R] adding by categories in a data frame???

[arun]

Hi,
dat1<- read.table(text="
name   number
a            2
a            3
b            5
b            7
c             9
c             1
",sep="",header=TRUE,stringsAsFactors=FALSE) 


aggregate(number~name,data=dat1,sum)
#  name number
#1    a      5
#2    b     12
#3    c     10

#or
library(plyr)
ddply(dat1,.(name),summarize,Sum_Number=sum(number))
#  name Sum_Number
#1    a          5
#2    b         12
#3    c         10

#or
library(data.table)
dt1<- data.table(dat1)

dt1[,list(Sum_Number=sum(number)),by=name]
#   name Sum_Number
#1:    a          5
#2:    b         12
#3:    c         10


##Speed comparison:
set.seed(1254)
name<- sample(letters,1e6,replace=TRUE)
number<- sample(1:10,1e6,replace=TRUE)

datTest<- data.frame(name,number,stringsAsFactors=FALSE)

system.time(res1<-aggregate(number~name,data=datTest,sum))
# user  system elapsed 
#  2.184   0.000   1.772 


system.time(res2<-ddply(datTest,.(name),summarize,Sum_Number=sum(number)))
# user  system elapsed 
#  0.256   0.000   0.227 

dtTest<- data.table(datTest)

system.time(res3<- dtTest[,list(Sum_Number=sum(number)),by=name])
#user  system elapsed 
#  0.084   0.000   0.066 
 names(res1)[2]<- names(res2)[2]
 identical(res1,res2)
#[1] TRUE
 res3New<- res3[order(name),]
identical(res1,as.data.frame(res3New))
#[1] TRUE




#to get descriptive statistics
by(dat1[,2],dat1[,1],summary)

#or
library(psych)
 describeBy(dat1[,2],dat1[,1],mat=TRUE)

A.K.


Hello. I have a big table and need to have descriptive statistics by sub-groups of data. 
For example: 
name   number 
a            2 
a            3 
b            5 
b            7 
c             9 
c             1 
How can I get/print a table that show the sum of numbers for each name? 
a = 5 
b = 12 
c = 10 
 Thank you!!!