crosstab - How can I count the frequency of an answer in R? -

i have db this:

id group drink 1        yes 2        no 3        na 4   b      no 5   b      no 6   b      yes 

and measure how many people of group drinks , how many people in group b drinks.

i using length(), function returns 3 (na being considered = yes). how can fix it?

table() 1 option:

db <- read.table(text = "id group drink 1        yes 2        no 3        na 4   b      no 5   b      no 6   b      yes", header = true)  with(db, table(drink)) with(db, table(group, drink))  > with(db, table(drink)) drink  no yes    3   2  > with(db, table(group, drink))      drink group no yes      1   1     b  2   1 

including na class achieved usena argument:

with(db, table(drink, usena = "ifany"))  > with(db, table(drink, usena = "ifany")) drink   no  yes <na>     3    2    1 

you can of course store objects returned table() , access them other matrix/array:

tab <- with(db, table(drink, usena = "ifany")) tab[1] tab2 <- with(db, table(group, drink, usena = "ifany")) tab2[,1] tab2[1,]  > tab <- with(db, table(drink, usena = "ifany")) > tab[1] no   3  > tab <- with(db, table(drink, usena = "ifany")) > tab[1] no   3  > tab2 <- with(db, table(group, drink, usena = "ifany")) > tab2[,1] b  1 2  > tab2[1,]   no  yes <na>     1    1    1