Re: [R] unwanted coercion using apply

From: David Winsemius <dwinsemius_at_comcast.net>
Date: Sun, 22 May 2011 15:40:09 -0400

On May 22, 2011, at 3:22 PM, Jeroen Ooms wrote:

>>
>> apply() operates on arrays and a data frame will be coerced to a
>> matrix
>> (which requires all elements to be of the same type). This is
>> documented in
>> ?apply.
>>
>
> Thanks, I was not aware of that. I implicitly assumed there would be a
> specific apply.data.frame.

  Because there is a constraint in R that all elements of a vector need to be of the same type.

>
>> This may not be elegant, but why not just use a loop:
>>
>
> The thing is that were are going to use this operation on a (very)
> large
> scale in a production environment, on datasets for which nrow >>
> ncol. So I
> would like the most efficient solution and if possibly, avoid
> looping over
> the rows.

But `apply` loops over rows, too. No speed advantage is being gained.

You may get better answers if you post a representative example that has types on which you will be operating. There may be vectorizable solutions that can operate column-wise.

>
> Thanks

-- 

David Winsemius, MD
West Hartford, CT

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Received on Sun 22 May 2011 - 19:42:58 GMT

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