If `trim`

is zero (the default), the arithmetic mean of the
values in `x`

is computed, as a numeric or complex vector of
length one. If `x`

is not logical (coerced to numeric), numeric
(including integer) or complex, `NA_real_`

is returned, with a warning.

If `trim`

is non-zero, a symmetrically trimmed mean is computed
with a fraction of `trim`

observations deleted from each end
before the mean is computed.