[R] Randomizing a dataframe

[Greg Snow]

Here is one approach (there are others, some that are probably better, but this can get you started):

1. rearrange your data so that every insect is a single row with 2 columns: the tree id and the species (this new dataset will have as many rows as the sum of the values in the old dataset).  The reshape package may be able to help with this step (you may also need the rep function).

2. randomly permute one of the 2 columns (see ?sample).

3. restructure the permuted data back to the original (the table function may be enough here, the reshape package will give more options).

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Mark Na
> Sent: Wednesday, July 08, 2009 9:54 AM
> To: r-help at r-project.org
> Subject: [R] Randomizing a dataframe
> 
> Hi R-helpers,
> 
> I have a dataframe (called data) with trees in rows (n=100) and insect
> species (n=10) in columns. My tree IDs are in a column called TREE and
> each
> species has a column labeled SPEC1, SPEC2, SPEC3, etc...
> 
> I wish to randomize the values in my dataframe such that row and column
> totals are held constant, i.e. in my randomized data each tree will
> have the
> same number of individual insects as in the real data (constant row
> totals)
> and each species will have the same number of individuals as in the
> real
> data (constant column totals).
> 
> I will eventually want to do this many times, but I would appreciate
> help
> getting started with the randomization.
> 
> Thank you, Mark Na
> 
> 	[[alternative HTML version deleted]]
> 
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