How to cross-tabulate two variables in R?

Question

This seems to be basic, but I wont get it. I am trying to compute the frequency table in R for the data as below

1 2 
2 1 
3 1  

I want to

Answer 1

The data:

df <- read.table(text = "1 2 
2 1 
3 1")

Calculate frequencies using table:

(If your object is a matrix, you could convert it to a data frame using as.data.frame before using table.)

tab <- table(df)

   V2
V1  1 2
  1 0 1
  2 1 0
  3 1 0

Write data with the function write.csv:

write.csv(tab, "tab.csv")

The resulting file:

"","1","2"
"1",0,1
"2",1,0
"3",1,0