[R] sapply returning list instead of matrix

Jeff Newmiller jdnewmil at dcn.davis.CA.us
Fri Jan 31 23:50:39 CET 2014

Pot, meet kettle. You claim to be able to read documentation, yet you don't reference knowledge gained or clarity lost from such activity in your question.

I think this is a case of inertia of history that we all have to live with at this point. If you thoroughly read the documentation for ?sapply you will encounter the vapply function, which will provide the reliability you want at the cost of some additional syntactic complexity.

Or not. I rarely use apply functions for arrays... if I can't vectorize my calculation, I preallocate my result array and use a for loop to fill it up. I don't have this problem with ddply.

BTW: Gmail is capable of sending plain text... but you might have to read some documentation to find out how.
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On January 31, 2014 2:22:00 PM PST, chris warth <cswarth at gmail.com> wrote:
>Hey thanks for the helpful snark, Bert.
>To everyone else, I apologize for neglecting to actually include the
>a <- function(i) { list(1) }
>b <- function(i) { list(1,2) }
>ll <- sapply(seq(3), a, simplfy="list")
>mm <- sapply(seq(3), b)
>> class(ll)
>[1] "list"
>> class(mm)
>[1] "matrix"
>I can read the documentation, I see why it happens, but who in their
>mind would design a function this way?  Can you imagine how many bugs
>lurking because people haven't yet hit the right set of input that is
>to cause sapply() to return a list instead of a matrix().
>The point is that having the type of return value depend on the length
>output from the applied function is simply madness.   It is a terrible
>design decision.  What is to be gained from the fact that I have to
>the type of value returned from sapply()?   I was hoping plyr::laply()
>would be better but it perpetuates the same bad interface.
>[so sorry for sending html, if that is what's happening.   I guess
>send html by default? ]
>On Fri, Jan 31, 2014 at 1:44 PM, Bert Gunter <gunter.berton at gene.com>
>> As you ignored the posting guide and posted in HTML, your "below"
>> didn't get through. So one can only guess that it has something to do
>> with (see ?sapply)
>> "Simplification in sapply is only attempted if X has length greater
>> than zero and if the return values from all elements of X are all of
>> the same (positive) length. If the common length is one the result is
>> a vector, and if greater than one is a matrix with a column
>> corresponding to each element of X. "
>> Return values most also be of the same type, also, obviously.
>> Cheers,
>> Bert
>> Bert Gunter
>> Genentech Nonclinical Biostatistics
>> (650) 467-7374
>> "Data is not information. Information is not knowledge. And knowledge
>> is certainly not wisdom."
>> H. Gilbert Welch
>> On Fri, Jan 31, 2014 at 1:36 PM, chris warth <cswarth at gmail.com>
>> > Can anyone suggest a rationale for why sapply() returns different
>> > (list and matrix) in the two examples below?   Is there any way to
>> > sapply() or any other apply() function to return a matrix in both
>> > simplify=TRUE doesn't change the outcome.
>> >
>> > I understand why it is happening, I just can't understand why such
>> > unpredictable behavior makes sense.
>> >
>> >         [[alternative HTML version deleted]]
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>	[[alternative HTML version deleted]]
>R-help at r-project.org mailing list
>PLEASE do read the posting guide
>and provide commented, minimal, self-contained, reproducible code.

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