R help - Jun 2008 - Frame from long to wide format

I have this frame in the long format which I want to convert to wide 
format.  There are three columns in the frame, the id for the rows in 
the wide format, the name of the column where the final value (the third 
column) is to be placed.

The complicating factor is that the long format is not complete in at 
least two ways, (a) there may be more than one reference to one cell in 
the wide format, in that case I want to use the last one, and (b) there 
may be no references to a cell in the wide format, and in that case I 
want the cell to be an NA.

I have looked at and done some experiments with the unstack () function, 
this does not seem to do what I want.  For instance, if there are more 
than one reference to a cell in the wide format, an extra row may be 
added or a list structure is produced.

What I want is to generate a frame in a "loose" manner, more or less
by
the generation of a frame with the number of rows corresponding to the 
individuals (unique values) and columns  (also unique values).  If there 
are no references in the long format to a given cell, then the value 
should be NA, if there are more than one, the last one should be used.

I can see (I think) how I could program this by the generation of a 
frame with the correct row and column names, fill that with NA's, and 
then use a for loop to assign a value for the long format to the correct 
cell in the frame.  That is not elegant, but would work.  Is it possible 
to be pointed towards alternatives?

The reshape function and even more powerful reshape package will probably do
what you want.

--
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 Tom Backer Johnsen
> Sent: Tuesday, June 10, 2008 2:59 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Frame from long to wide format
>
> I have this frame in the long format which I want to convert
> to wide format.  There are three columns in the frame, the id
> for the rows in the wide format, the name of the column where
> the final value (the third
> column) is to be placed.
>
> The complicating factor is that the long format is not
> complete in at least two ways, (a) there may be more than one
> reference to one cell in the wide format, in that case I want
> to use the last one, and (b) there may be no references to a
> cell in the wide format, and in that case I want the cell to be an NA.
>
> I have looked at and done some experiments with the unstack
> () function, this does not seem to do what I want.  For
> instance, if there are more than one reference to a cell in
> the wide format, an extra row may be added or a list
> structure is produced.
>
> What I want is to generate a frame in a "loose" manner, more
> or less by the generation of a frame with the number of rows
> corresponding to the individuals (unique values) and columns
> (also unique values).  If there are no references in the long
> format to a given cell, then the value should be NA, if there
> are more than one, the last one should be used.
>
> I can see (I think) how I could program this by the
> generation of a frame with the correct row and column names,
> fill that with NA's, and then use a for loop to assign a
> value for the long format to the correct cell in the frame.
> That is not elegant, but would work.  Is it possible to be
> pointed towards alternatives?
>
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