A generic function for computing the variance of an object.

```
variance(x, ...)
# S3 method for class 'numeric'
variance(x, ...)
# S3 method for class 'matrix'
variance(x, ...)
# S3 method for class 'numeric'
covariance(x, ...)
```

## Arguments

- x
An object.

- ...
Additional arguments used by methods.

## Details

The implementation of `variance()`

for numeric variables coerces the input to
a vector then uses `stats::var()`

to compute the variance. This means that,
unlike `stats::var()`

, if `variance()`

is passed a matrix or a 2-dimensional
array, it will still return the variance (`stats::var()`

returns the
covariance matrix in that case).