with関数とby関数を使おう
With
The with( ) function applys an expression to a dataset. It is similar to DATA= in SAS.
# with(data, expression)
# example applying a t-test to dataframe
mydata
with(mydata, t.test(y1,y2)
By
The by( ) function applys a function to each level of a factor or factors. It is similar to BY processing in SAS.
# by(data, factorlist, function)
# example apply a t-test separately
for men and women
by(mydata, gender, t.test(y1,y2))