Help with NaN when 0 divided by 0

 "%/0%" <- function(x,y) { res <- x / y ; res[ is.na(res) ] <- 0;
return(res) }

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Jennifer Sabatier
Sent: Wednesday, August 01, 2012 7:18 AM
To: David Winsemius
Cc: r-help at r-project.org
Subject: Re: [R] Help with NaN when 0 divided by 0

Hi Everyone,

Thanks so much for all your suggestions!  All of these worked but David's
was best suited for my purposes, considering it was something happens
sporadically.

I don't do expenditure analyses often as I mostly do run of the mill survey
analysis, but this will come in handy for the once or twice a year I do
this.

Jen

On Tue, Jul 31, 2012 at 5:19 PM, David Winsemius <dwinsemius at comcast.net>wrote:

On Jul 31, 2012, at 1:23 PM, Jennifer Sabatier wrote:

 Hi All,

I have some data where I am doing fairly simple calculations, nothing more
than adding, subtracting, multiplying and dividing.



I'm running into a problem when I divide one variable by another and when
they're both 0 I get NaN. I realize that if you divide a non-zero by 0
then
you get Inf, which is, of course, correct.  But in my case I never get
Inf,
just NaN because of the structure of my dataset.



Here's a dumb example:



var1 <- c(0, 500, 5379, 0, 1500, 1750)

var2 <- c(0, 36, 100, 0, 10, 5)



var1/var2

It's possible to define new infix operators (although I have forgotten
which help page describes this in more detail and I cannot seem to find it
right now):

 "%/0%" <- function(x,y) { res <- x / y ; res[ is.na(res) ] <- 0;
return(res) }

# You cannot use %/% because it is already used for integer division. I
guess you could use "//", but to me that looks too much like "||" which is
the single-value-OR. You could also use "%div0%".

 var1 %/0% var2

#[1]   0.00000  13.88889  53.79000   0.00000 150.00000 350.00000

If this is a regular need, you can put this in a .profile file or a
package. See:

?Startup

--

 I realize the NaNs are logical, but for my purposes this should just be 0

because I am calculating expenditures and if you spent no money in one
sub-area and none in the whole area then you don't have an expenditure at
all, so it should be 0.  And since R doesn't like adding NA's or NaN's to
anything, I'd rather just have this be 0 so that my future calculations,
such as adding up expenditure, is simple.


Is there an easy way to avoid the NaN's, something a non-programmer (ie,
the person I am handing this code off to) would understand?

Thanks,


Jen

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David Winsemius, MD
Alameda, CA, USA

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