[R] Data frame: how to create list of row max?

[Chuck Cleland]

Johannes Graumann wrote:
> Dear all,
> 
> Can anyone please shed some light onto how to do this?
> 
> This will give me all "intensity" columsn in my data frame:
> intensityindeces <- grep("^Intensity",names(dataframe),value=TRUE)
> 
> This will give me the maximum intensity for the first row:
> intensityone <- max(dataframe[1,intensityindeces])
> 
> What I'm now looking for is how to dfo this for the whole data frame. Should
> yield a list of maximum intensities of all rows.
> Can't figure it out ... please nudge me where I need to go.

  If you want the values themselves:

apply(dataframe[,intensityindeces], 1, max)

  If you want the column in which the max appears:

apply(dataframe[,intensityindeces], 1, which.max)

?apply

> Thanks, Joh
> 
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Chuck Cleland, Ph.D.
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