checking even/odd in R

-----Original Message-----
From: Albyn Jones [mailto:jones at reed.edu] 
Sent: Sunday, December 03, 2006 9:42 PM
To: John Fox
Cc: bob at statland.org; 'Yeasmin Khandakar'; 'R-sig-teaching'
Subject: Re: [R-sig-teaching] checking even/odd in R

One solution for the exact equality problem is to start by 
rounding or truncating to an integer, depending of course on 
what the origin of the dataset was, and the point of the 
operation.  The sign doesn't matter;

-3 %% 2

[1] 1


floor(x) rounds down to an integer
ceiling(x) rounds up
round(x) rounds to the nearest integer, rounding to an even integer
         in case of ties

albyn

Quoting John Fox <jfox at mcmaster.ca>:

Dear Robert and Yeasmin,

You could test that the number mod 2 is 0; e.g.,

(1:10 %% 2) == 0

[1] FALSE  TRUE FALSE  TRUE FALSE  TRUE FALSE  TRUE FALSE  TRUE

A potential problem is that testing exact equality is 

risky, so you're 

probably better off checking that abs(x) %% 2 is less than 

some very 

small number such as sqrt(.Machine$double.eps).

I hope this helps,
John

--------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox
--------------------------------

-----Original Message-----
From: r-sig-teaching-bounces at r-project.org
[mailto:r-sig-teaching-bounces at r-project.org] On Behalf Of 

Robert W. 

Hayden
Sent: Sunday, December 03, 2006 8:24 PM
To: Yeasmin Khandakar
Cc: R-sig-teaching
Subject: Re: [R-sig-teaching] checking even/odd in R


I do not know of anything specific to r but standard programming 
tricks may do it.  For example, if the number is x, compute y=x/2, 
let z be y rounded to the nearest whole number, and check 

if y=z.  If 

it does, x is even.  There may be rounding issues; I doubt 

R stores 

data as integers.  You might have to do this in an 

environment that 

sees the numbers as integers -- or text.  AWK comes to mind.

You may also want code to check for x values like 23.456.

Dear all,

I'm in search for a function which can be used to check 

whether a 

numeriacl value (say, x) is even/odd.
Any help is highly appreciated.

Thanks
Yeasmin

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