[R] R- transform data frame into matrix

[Thorsten Raff]

Thank you very much,

looks rather simple when viewed from behind :(

> Try this also:
> xtabs(values ~ diagnosis + marker, data=dataframe)


> You can make your examples self-running by providing fake data for
> diagnosis, e.g. using letters[] instead of diagnosis. In addition, note that
> your cbind has an awkward side effect by converting everything to character 
> as the least common denominator for the variables in a matrix.

> For real work, use reshape with its frightening number of parameters. If you
> don't understand that function at the seventh reading, stay cool: it's not
> your fault. You might also try package reshape, but it is not much easier
> for occasional use.


> Dieter

> diagnosis <- as.factor(rep(letters[1:3], 3))
> marker <- as.factor(gl(3,3))
> values <- rnorm(9)
> dataframe <- data.frame(diagnosis=diagnosis, marker=marker, values=values)
> dataframe <- dataframe[c(1:5, 7:9), ]
> reshape(dataframe,idvar="diagnosis",direction="wide",timevar="marker")

>> I have the problem that I want to transform a dataframe as generated by
>> 
>> diagnosis <- rep(diagnosis[1:3], 3)
>> marker <- gl(3,3)
>> values <- rnorm(9)
>> dataframe <- cbind(diagnosis, marker, values)
>> dataframe <- dataframe[c(1:5, 7:9), ]
>> 
>> into a matrix where levels(diagnosis) is indicating the rows of the matrix, 
>> levels(marker) the columns and values are the actual content of the matrix. 
>> However, as can been seen in the dataframe, some observations are missing
>> and 
>> should result in <NAs> in the resulting matrix, giving a result like this:
>> marker              1         2         3
>> diagnosis1      value   value   value
>> diagnosis2      value   value   value
>> diagnosis3      value      NA    value
>> 

-- 
Thorsten Raff
2nd Medical Department,
University Hospital Schleswig-Holstein, Campus Kiel
Chemnitzstraße 33
24116 Kiel
GERMANY

phone: +49 431 1697-5234
fax:   +49 431 1697-1264

email: t.raff<at>med2.uni-kiel.de
web:   www.uk-s-h.de

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