[R] Creating dataframe of all possible variable combinations

[Rolf Turner]

On 26/03/2010, at 9:22 AM, Hosack, Michael wrote:

> Hello,
> 
> I need to create a dataframe containing all possible combinations of 
> three variables: SITE (101,102,103,104), WDAY (MON,TUE,WED,THR,FRI),
> and TOD (MORN, AFTN). There should be a total of 40 unique combinations
> in my dataframe. I used expand.grid() successfully(?) to create my 
> dataframe, but then when I went to order it by SITE, the resultant 
> dataframe only contained four rows, one for each site. There must 
> be something about this function that I don't understand. Any advice
> would be appreciated.

Works for me. I used:

xxx <- expand.grid(SITE=SITE,WDAY=WDAY,TOD=TOD)
yyy <- xxx[order(xxx$SITE),]

I expect you used:

yyy <- xxx[order(SITE),]

In the foregoing, SITE is the length-4 vector in your global environment, not
the length-40 column of xxx.  So ``naturally'' you get a result with 4 rows.

	cheers,

		Rolf Turner

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