[R] calculating mean excluding zeros
sarah.goslee at gmail.com
Wed Jul 20 02:06:28 CEST 2011
On Tue, Jul 19, 2011 at 5:20 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> Thanks a lot, Sarah.
> I assume, if the values against which I am comparing are REALLY zero
> ("0") - then even the first one (mean(testvec[testvec != 0])) should
> work, right?
Well, yes. But what's "really" zero?
> ((.2 + .1) - .3) == 0
> all.equal(((.2 + .1) - .3), 0)
"0" is a string, and string comparison is a different issue, not
subject to machine precision.
> On Tue, Jul 19, 2011 at 4:56 PM, Sarah Goslee <sarah.goslee at gmail.com> wrote:
>> In the more general case, that approach is prone to machine precision
>> error (FAQ 7.31).
>> Here's a clunky but safer alternative:
>>> testvec <- sample(0:10, 100, replace=TRUE)
>>  4.31
>>> mean(testvec[testvec != 0])
>>  4.842697
>>> mean(testvec[!sapply(testvec, function(x)isTRUE(all.equal(x, 0)))])
>>  4.842697
>> (Is there an elementwise equivalent to all.equal() that I'm missing?)
>> On Tue, Jul 19, 2011 at 4:48 PM, Weidong Gu <anopheles123 at gmail.com> wrote:
>>> You can do it by subsetting or indexing
>>>  8.052215
>>>  10.46788
>>> Weidong Gu
>>> On Tue, Jul 19, 2011 at 4:36 PM, Dimitri Liakhovitski
>>> <dimitri.liakhovitski at gmail.com> wrote:
>>>> Sorry if it's been discussed before - don't seem to find it.
>>>> I'd like to calculate a mean while ignoring zeros.
>>>> "mean" doesn't seem to have an option for that.
>>>> Any other function/package that could do it?
>>>> Thanks for a pointer!
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