Converting a numerical (double) into an integer
Number literals that look like integers (for example 4) are internally stored as doubles. as.integer() converts them to integers.
If a number literal is suffixed with an L, its type is integer:
four <- 4;
typeof(four);
#
# "double"
four_int <- as.integer(four);
typeof(four_int);
#
# "integer"
five <- 5L;
typeof(five);
#
# "integer"
Applying as.integer on a factor
Factors are internally stored as a
vector of integers. Applying
as.integer(…) on a factor displays these integers:
fac <- factor(c('foo', 'bar', 'foo', 'baz', 'bar'));
levels(fac);
#
# "bar" "baz" "foo"
as.integer(fac);
#
# 3 1 3 2 1
Applying as.integer on a POSIXct object
If
as.integer() is applied on a
POSIXct object, it returns the number of seconds since 1970-01-01:
as.integer(ISOdate(1970, 1, 1, 0, 0, 0))
# [1] 0
as.integer(ISOdate(1970, 1, 1, 0, 0, 1))
# [1] 1
as.integer(ISOdate(1970, 1, 1, 0, 1, 0))
# [1] 60
as.integer(ISOdate(1971, 1, 1, 0, 0, 0)) / 24 / 60 / 60
# [1] 365