[R] / Operator not meaningful for factors

[Prof Brian Ripley]

The mode of a factor is numeric, so your test does not do what you think 
it does.

is.numeric() is the recommended test of a vector being numeric.  I have no 
idea where you got the idea that mode() was a useful test (perhaps you 
could give us the reference you used), but it rather rarely is (typeof is 
usually more informative).

>From the summary quoted, Price is clearly a factor.  Test it with 
is.factor.

On Sun, 15 Jan 2006, Vivek Satsangi wrote:

> Folks,
> I have a very basic question. The solution eludes me perhaps because
> of my own lack of creativity. I am not attaching a fully reproducible
> session because the issue may well be becuase of the way the data file
> is, and the data file is large (and I don't know whether I can legally
> distribute it). If people can suggest things that might be wrong in my
> data or the way that I am reading it, I would be most grateful.
>
> I get the following error message in the session quoted at the end of
> this email:
> / not meaningful for factors in: Ops.factor(BookValuePS, Price)
>
> As you can see in that some session, I check that the two vectors
> being divided are numeric.

(see the request above for your reference here)

> I also check that the divisor is not 0 at any index. I also believe that 
> this is not because of the NA's in the data. My question is, what are 
> other "problems" that can cause the / operator to not be meaningful?

Why not test for factor, since that is what the very helpful error message 
told you the problem was?

> I did try some simple examples to try to get the same error. However,
> I am not sure how to put the same NA's that one  gets from
> read.table() into a vector:
>> a <- c(1, 2, 3, NA);
>> a
> [1]  1  2  3 NA
>> b <- c( 1, 2, 3, 4);
>> c <- b / a;
>> b
> [1] 1 2 3 4
>> a <- c(1, 2, 3, );
>> c <- b/a;
> Warning message:
> longer object length
>        is not a multiple of shorter object length in: b/a
>
>
> ******** Quoted Session below ********
> > explainPriceSimplified <- read.table("combinedClean.csv",
> +                            sep = ",", header=TRUE);
>> attach(explainPriceSimplified);
>> summary(explainPriceSimplified);
>     Symbol           Date              Price            EPS
>   BookValuePS
> XL     :   98   Min.   :19870630   22     :   61   Min.   :-1.401e+05
>  Min.   :-6.901e+05
> ZION   :   97   1st Qu.:19910930   26.5   :   61   1st Qu.: 4.650e-01
>  1st Qu.: 3.892e+00
> YRCW   :   72   Median :19960331   27.5   :   58   Median : 1.060e+00
>  Median : 7.882e+00
> AA     :   71   Mean   :19957688   30     :   58   Mean   :-1.534e+01
>  Mean   : 1.515e+02
> ABS    :   71   3rd Qu.:20001231   25     :   56   3rd Qu.: 1.890e+00
>  3rd Qu.: 1.444e+01
> ABT    :   71   Max.   :20041231   (Other):29561   Max.   : 5.309e+03
>  Max.   : 3.366e+06
> (Other):29624                      NA's   :  249   NA's   : 2.460e+02
>  NA's   : 4.760e+02
> FiscalQuarterRep    F12MRet
> 2004/2F:  482    Min.   :-100.00
> 2003/4F:  471    1st Qu.:  -8.82
> 2004/1F:  470    Median :  10.57
> 2004/3F:  470    Mean   :  13.36
> 2003/3F:  464    3rd Qu.:  31.12
> 2003/2F:  463    Max.   :4700.00
> (Other):27284    NA's   : 463.00
>> mode(Price)
> [1] "numeric"
>> mode(EPS)
> [1] "numeric"
>> mode(BookValuePS)
> [1] "numeric"
>> BP <- BookValuePS / Price ;
> Warning message:
> / not meaningful for factors in: Ops.factor(BookValuePS, Price)
>> which(Price==0)
> numeric(0)

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595