# [Rd] meaning of "trim" in mean()

Patrick Burns pburns at pburns.seanet.com
Sun Oct 28 09:43:06 CET 2007

```If the sentence in question were amended to:

Values of trim outside that range ...

then I think it would rule out the misinterpretation of
the sentence.

Pat

Prof Brian Ripley wrote:

>There is only one _range_ mentioned, (0, 0.5).  I don't see how you can
>construe 'that range' to be a reference to anything other than (0, 0.5).
>
>And why do you suppose the description for argument 'trim' is referring to
>'values' of a different argument?
>
>It is telling you what happens for values of trim < 0 or > 0.5: that is
>not information that it is appropriate to excise.
>
>
>On Thu, 25 Oct 2007, Peter Dalgaard wrote:
>
>
>
>>Liaw, Andy wrote:
>>
>>
>>>(I see this in both R-patched r43124 and R-devel r43233.)
>>>In the Argument section of ?mean:
>>>
>>>trim     the fraction (0 to 0.5) of observations to be trimmed from each
>>>end of x before the mean is computed. Values outside that range are
>>>taken as the nearest endpoint.
>>>
>>>Then in the Value section:
>>>
>>>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.
>>>
>>>The description in "trim" to me sounds like Windsorizing, rather than
>>>trimming.  Should that be edited?
>>>
>>>
>>>
>>>
>>I think so:
>>
>>
>>
>>>x <- sort(rnorm(10))
>>>mean(x,trim=.1)
>>>
>>>
>>[1] -0.6387413
>>
>>
>>>mean(x[2:9])
>>>
>>>
>>[1] -0.6387413
>>
>>
>>>mean(x[c(2,2:9,9)]) # Winsorizing
>>>
>>>
>>[1] -0.6204222
>>
>>So yes, it is trimming, not Winsorizing, and the last sentence in the
>>description of "trim" is misleading and should be, well..., trimmed.
>>
>>
>>
>>
>
>
>

```