Count frequency of a vector
table applied on a
vector counts the frequencies of its elements
vec <- c('ABC', 'DEF', 'ABC', 'ABC', 'GHI', 'DEF', 'ABC')
table(vec)
#
# vec
# ABC DEF GHI
# 4 2 1
table(factor(vec))
#
#
# ABC DEF GHI
# 4 2 1
Contigency table
If two vectors are passed to the
table function, it returns a
contingency table (aka cross tabulation)
contigency_table <- table(c('AAA', 'AAA', 'BBB', 'AAA', 'AAA', 'CCC', 'BBB', 'BBB', 'AAA'),
c('yyy', 'yyy', 'qqq', 'yyy', 'qqq', 'iii', 'yyy', 'qqq', 'iii')
);
contigency_table;
#
# iii qqq yyy
# AAA 1 1 3
# BBB 0 2 1
# CCC 1 0 0
attributes(contigency_table);
# $dim
# [1] 3 3
#
# $dimnames
# $dimnames[[1]]
# [1] "AAA" "BBB" "CCC"
#
# $dimnames[[2]]
# [1] "iii" "qqq" "yyy"
#
#
# $class
# [1] "table"
N-Way contigency table
It is also possible to create a *three-way contigency table (or more generally, an n-way contigency table):
n_way_ct <- table(c("AAA", "AAA", "BBB", "AAA", "AAA", "CCC", "BBB", "BBB", "AAA"),
c("yyy", "yyy", "qqq", "yyy", "qqq", "iii", "yyy", "qqq", "iii"),
c("___", "###", "___", "___", "###", "___", "___", "###", "???")
);
n_way_ct;
#
# , , = ###
#
#
# iii qqq yyy
# AAA 0 1 1
# BBB 0 1 0
# CCC 0 0 0
#
# , , = ???
#
#
# iii qqq yyy
# AAA 1 0 0
# BBB 0 0 0
# CCC 0 0 0
#
# , , = ___
#
#
# iii qqq yyy
# AAA 0 0 2
# BBB 0 1 1
# CCC 1 0 0