Match()

print(match(5, c(2,7,5,3))) #  5 is in 3rd place
print(seq(from=1,to=3,by=.5) %in% 1:3)

[1] 3
[1]  TRUE FALSE  TRUE FALSE  TRUE

The match function find the first occurrence of the first argument in the second argument:

match(x=3, table=2:6)

[1] 2

The nomatch argument

By default match returns NA if no match for x is found in table. You can change this by using the nomatch argument:

match(1, 4:8, nomatch=-1)

[1] -1

The %in% operator

According to the documentation the following two lines are equivalent:

match(x, table, nomatch = 0) > 0
x %in% table

Using %in% can be more readable and provides you with a list of TRUE/FALSE values.