R help - Feb 2013 - e1071::skewness and psych::skew return NaN

Hello everyone,

Does anyone know what would cause the skewness() function (from
e1071), as well as skew() from psych, to return a value of NaN?

I have a vector of positively-skewed data
(https://docs.google.com/file/d/0B6-m45Jvl3ZmYzlHRVRHRURzbVk/edit?usp=sharing)
which these functions return a value for like normal:
> skewness( data ) # returns 1.400405
but when I instead give those functions the log-transformed data they return NaN
> skewness( log( data ) ) #returns NaN
The same occurs when I feed the function data transformed by reflected
reciprocal
> skewness( max(data) - 1/data ) ) #returns NaN
The vector has no missing values (and if it did, I would get NA rather
than NaN, and the function wouldn't return a number when I give it the
raw data).

Best,
Steve

--
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/

Hi everyone,

Please disregard my last message, I found a 0 in the vector, which is
what was causing problems with the log and reciprocal data.

Best,
Steve

On Wed, Feb 13, 2013 at 10:55 AM, Stephen Politzer-Ahles
<politzerahless at gmail.com> wrote:
> Hello everyone,
>
> Does anyone know what would cause the skewness() function (from
> e1071), as well as skew() from psych, to return a value of NaN?
>
> I have a vector of positively-skewed data
>
(https://docs.google.com/file/d/0B6-m45Jvl3ZmYzlHRVRHRURzbVk/edit?usp=sharing)
> which these functions return a value for like normal:
>
>> skewness( data ) # returns 1.400405
>
> but when I instead give those functions the log-transformed data they
return NaN
>
>> skewness( log( data ) ) #returns NaN
>
> The same occurs when I feed the function data transformed by reflected
> reciprocal
>
>> skewness( max(data) - 1/data ) ) #returns NaN
>
> The vector has no missing values (and if it did, I would get NA rather
> than NaN, and the function wouldn't return a number when I give it the
> raw data).
>
> Best,
> Steve
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/


-- 
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/

Hello,

That value means that some values of your data are negative or zero. A 
simple inspection shows that

any(dat < 0)  # FALSE
any(dat == 0) # TRUE

Solution: don't log your data


Hope this helps,

Rui Barradas

Em 13-02-2013 16:55, Stephen Politzer-Ahles escreveu:
> Hello everyone,
>
> Does anyone know what would cause the skewness() function (from
> e1071), as well as skew() from psych, to return a value of NaN?
>
> I have a vector of positively-skewed data
>
(https://docs.google.com/file/d/0B6-m45Jvl3ZmYzlHRVRHRURzbVk/edit?usp=sharing)
> which these functions return a value for like normal:
>
>> skewness( data ) # returns 1.400405
>
> but when I instead give those functions the log-transformed data they
return NaN
>
>> skewness( log( data ) ) #returns NaN
>
> The same occurs when I feed the function data transformed by reflected
> reciprocal
>
>> skewness( max(data) - 1/data ) ) #returns NaN
>
> The vector has no missing values (and if it did, I would get NA rather
> than NaN, and the function wouldn't return a number when I give it the
> raw data).
>
> Best,
> Steve
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/
>
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