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

by 
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

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