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

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

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