Creates or coerces objects of type `"numeric"`

.
`is.numeric`

is a more general test of an object being
interpretable as numbers.

```
numeric(length = 0)
as.numeric(x, …)
is.numeric(x)
```

length

A non-negative integer specifying the desired length. Double values will be coerced to integer: supplying an argument of length other than one is an error.

x

object to be coerced or tested.

…

further arguments passed to or from other methods.

for `numeric`

and `as.numeric`

see `double`

.

The default method for `is.numeric`

returns `TRUE`

if its argument is of mode `"numeric"`

(type `"double"`

or type `"integer"`

) and not a
factor, and `FALSE`

otherwise. That is,
`is.integer(x) || is.double(x)`

, or
`(mode(x) == "numeric") && !is.factor(x)`

.

If `x`

is a `factor`

, `as.numeric`

will return
the underlying numeric (integer) representation, which is often
meaningless as it may not correspond to the `factor`

`levels`

, see the ‘Warning’ section in
`factor`

(and the 2nd example below).

`as.numeric`

and `is.numeric`

are internally S4 generic and
so methods can be set for them *via* `setMethod`

.

To ensure that `as.numeric`

and `as.double`

remain identical, S4 methods can only be set for `as.numeric`

.

It is a historical anomaly that R has two names for its
floating-point vectors, `double`

and `numeric`

(and formerly had `real`

).

`double`

is the name of the type.
`numeric`

is the name of the mode and also of the implicit
class. As an S4 formal class, use `"numeric"`

.

The potential confusion is that R has used *mode*
`"numeric"`

to mean ‘double or integer’, which conflicts
with the S4 usage. Thus `is.numeric`

tests the mode, not the
class, but `as.numeric`

(which is identical to `as.double`

)
coerces to the class.

`numeric`

is identical to `double`

(and `real`

).
It creates a double-precision vector of the specified length with each
element equal to `0`

.

`as.numeric`

is a generic function, but S3 methods must be
written for `as.double`

. It is identical to `as.double`

.

`is.numeric`

is an internal generic `primitive`

function: you can write methods to handle specific classes of objects,
see InternalMethods. It is **not** the same as
`is.double`

. Factors are handled by the default method,
and there are methods for classes `"Date"`

,
`"POSIXt"`

and `"difftime"`

(all of which
return false). Methods for `is.numeric`

should only return true
if the base type of the class is `double`

or `integer`

*and* values can reasonably be regarded as numeric
(e.g., arithmetic on them makes sense, and comparison should be done
via the base type).

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
*The New S Language*.
Wadsworth & Brooks/Cole.

# NOT RUN { as.numeric(c("-.1"," 2.7 ","B")) # (-0.1, 2.7, NA) + warning as.numeric(factor(5:10)) # not what you'd expect f <- factor(1:5) ## what you typically meant and want: as.numeric(as.character(f)) ## the same, considerably (for long factors) more efficient: as.numeric(levels(f))[f] # }