how to calculate mean/median per group in a dataframe in r [duplicate]

Question

I have a dataframe recording how much money a costomer spend in detail like the following:

custid, value
1,  1
1,  3
1,  2
1,  5
1,  4
1,  1
2,  1
2,  10
3,  1
3,  2
3,  5

How to calcuate the charicteristics using mean,max,median,std, etc like the following? Use some apply function? And how?

custid, mean, max,min,median,std
1,  ....
2,....
3,....

Answer 1

library(dplyr)
dat%>%
group_by(custid)%>% 
summarise(Mean=mean(value), Max=max(value), Min=min(value), Median=median(value), Std=sd(value))
#  custid     Mean Max Min Median      Std
#1      1 2.666667   5   1    2.5 1.632993
#2      2 5.500000  10   1    5.5 6.363961
#3      3 2.666667   5   1    2.0 2.081666

For bigger datasets, data.table would be faster

setDT(dat)[,list(Mean=mean(value), Max=max(value), Min=min(value), Median=as.numeric(median(value)), Std=sd(value)), by=custid]
#   custid     Mean Max Min Median      Std
#1:      1 2.666667   5   1    2.5 1.632993
#2:      2 5.500000  10   1    5.5 6.363961
#3:      3 2.666667   5   1    2.0 2.081666