[R] Bug in by() function which works for some FUN argument and does not work for others

[Jim Lemon]

Hi Dr Singh,
The object mtcars is a data frame and the mean is not defined for a
data frame. If you try it on a component of the data frame for which
mean is defined:

 by(mtcars$mpg,mtcars$am,mean)
mtcars$am: 0
[1] 17.14737
------------------------------------------------------------
mtcars$am: 1
[1] 24.39231

Jim

On Fri, Apr 15, 2016 at 6:14 AM, Akhilesh Singh
<akhileshsingh.igkv at gmail.com> wrote:
> Dear Sirs,
>
> I am Professor at Indira Gandhi Krishi Vishwavidyalaya, Raipur,
> Chhattisgarh, India.
>
> While taking classes, I found the *by() *function producing following error
> when I use FUN=mean or median and some other functions, however,
> FUN=summary works.
>
> Given below is the output of the example I used on a built-in dataset
> "mtcars", along with error message reproduced herewith:
>
>> by(data=mtcars, INDICES=list(mtcars$am), FUN=mean)
> : 0
> [1] NA
> ------------------------------------------------------------
> : 1
> [1] NA
> Warning messages:
> 1: In mean.default(data[x, , drop = FALSE], ...) :
>   argument is not numeric or logical: returning NA
> 2: In mean.default(data[x, , drop = FALSE], ...) :
>   argument is not numeric or logical: returning NA
>
> However, the same by() function works for FUN=summary, given below is the
> output:
>
>> by(data=mtcars, INDICES=list(mtcars$am), FUN=summary)
> : 0
>       mpg             cyl             disp             hp
>  Min.   :10.40   Min.   :4.000   Min.   :120.1   Min.   : 62.0
>  1st Qu.:14.95   1st Qu.:6.000   1st Qu.:196.3   1st Qu.:116.5
>  Median :17.30   Median :8.000   Median :275.8   Median :175.0
>  Mean   :17.15   Mean   :6.947   Mean   :290.4   Mean   :160.3
>  3rd Qu.:19.20   3rd Qu.:8.000   3rd Qu.:360.0   3rd Qu.:192.5
>  Max.   :24.40   Max.   :8.000   Max.   :472.0   Max.   :245.0
>       drat             wt             qsec             vs               am
>
>  Min.   :2.760   Min.   :2.465   Min.   :15.41   Min.   :0.0000   Min.   :0
>
>  1st Qu.:3.070   1st Qu.:3.438   1st Qu.:17.18   1st Qu.:0.0000   1st Qu.:0
>
>  Median :3.150   Median :3.520   Median :17.82   Median :0.0000   Median :0
>
>  Mean   :3.286   Mean   :3.769   Mean   :18.18   Mean   :0.3684   Mean   :0
>
>  3rd Qu.:3.695   3rd Qu.:3.842   3rd Qu.:19.17   3rd Qu.:1.0000   3rd Qu.:0
>
>  Max.   :3.920   Max.   :5.424   Max.   :22.90   Max.   :1.0000   Max.   :0
>
>       gear            carb
>  Min.   :3.000   Min.   :1.000
>  1st Qu.:3.000   1st Qu.:2.000
>  Median :3.000   Median :3.000
>  Mean   :3.211   Mean   :2.737
>  3rd Qu.:3.000   3rd Qu.:4.000
>  Max.   :4.000   Max.   :4.000
> ------------------------------------------------------------
> : 1
>       mpg             cyl             disp             hp             drat
>
>  Min.   :15.00   Min.   :4.000   Min.   : 71.1   Min.   : 52.0   Min.
> :3.54
>  1st Qu.:21.00   1st Qu.:4.000   1st Qu.: 79.0   1st Qu.: 66.0   1st
> Qu.:3.85
>  Median :22.80   Median :4.000   Median :120.3   Median :109.0   Median
> :4.08
>  Mean   :24.39   Mean   :5.077   Mean   :143.5   Mean   :126.8   Mean
> :4.05
>  3rd Qu.:30.40   3rd Qu.:6.000   3rd Qu.:160.0   3rd Qu.:113.0   3rd
> Qu.:4.22
>  Max.   :33.90   Max.   :8.000   Max.   :351.0   Max.   :335.0   Max.
> :4.93
>        wt             qsec             vs               am         gear
>
>  Min.   :1.513   Min.   :14.50   Min.   :0.0000   Min.   :1   Min.   :4.000
>
>  1st Qu.:1.935   1st Qu.:16.46   1st Qu.:0.0000   1st Qu.:1   1st Qu.:4.000
>
>  Median :2.320   Median :17.02   Median :1.0000   Median :1   Median :4.000
>
>  Mean   :2.411   Mean   :17.36   Mean   :0.5385   Mean   :1   Mean   :4.385
>
>  3rd Qu.:2.780   3rd Qu.:18.61   3rd Qu.:1.0000   3rd Qu.:1   3rd Qu.:5.000
>
>  Max.   :3.570   Max.   :19.90   Max.   :1.0000   Max.   :1   Max.   :5.000
>
>       carb
>  Min.   :1.000
>  1st Qu.:1.000
>  Median :2.000
>  Mean   :2.923
>  3rd Qu.:4.000
>  Max.   :8.000
>>
>
> I am using the latest version of *R-3.2.4 on Windows*, however, this error
> is being generated in the previous version too,
>
> Hope this reporting will get serious attention in debugging.
>
> With best regards,
>
> Dr. A.K. Singh
> Head, Department of Agril. Statistics
> Indira Gandhi Krishi Vishwavidyalaya, Raipur
> Chhattisgarh, India, PIN-492012
> Mobile: +919752620740
> Email: akhileshsingh.igkv at gmail.com
>
>         [[alternative HTML version deleted]]
>
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