The basic method for view a function's source code is input its name in R console without paranthesis:
> mean
function (x, ...)
UseMethod("mean")
<bytecode: 0x611edd8>
<environment: namespace:base>
The above output means this function is a generic function,
which represents a group of functions.
You can list this group with methods() function:
> methods(mean)
[1] mean.Date mean.default mean.difftime mean.POSIXct mean.POSIXlt
see '?methods' for accessing help and source code
The final step is use getAnywhere() to view the souce codes
(here we choose the function mean.default):
> getAnywhere(mean.default())
A single object matching ‘mean.default’ was found
It was found in the following places
package:base
registered S3 method for mean from namespace base
namespace:base
with value
function (x, trim = 0, na.rm = FALSE, ...)
{
if (!is.numeric(x) && !is.complex(x) && !is.logical(x)) {
warning("argument is not numeric or logical: returning NA")
return(NA_real_)
}
if (na.rm)
x <- x[!is.na(x)]
if (!is.numeric(trim) || length(trim) != 1L)
stop("'trim' must be numeric of length one")
n <- length(x)
if (trim > 0 && n) {
if (is.complex(x))
stop("trimmed means are not defined for complex data")
if (anyNA(x))
return(NA_real_)
if (trim >= 0.5)
return(stats::median(x, na.rm = FALSE))
lo <- floor(n * trim) + 1
hi <- n + 1 - lo
x <- sort.int(x, partial = unique(c(lo, hi)))[lo:hi]
}
.Internal(mean(x))
}
<bytecode: 0x611e5e0>
<environment: namespace:base>
But this method doesn't work for stats::hatvalues function.
Read the doc of hatvalues you can find it's just a wrapper of lm.influence,
you can verify this through the following codes:
> mdl <- lm(hp ~ cyl + mpg, data = mtcars)
> hats <- hatvalues(mdl)
> infs <- lm.influence(mdl)
> sum(hats - infs$hat)
0
Get the source of lm.influence(): getAnywhere(lm.influence)
You can see the res$hat in the source codes is just the \(h\) vector.