Jeff,
Could you please tell me which part of the guide that I didn't follow?
I provide a piece of code that can run in R, producing the problem and I also
provided my results.
Other people wanted to help me to learn more so asked me about more details. I
replied very carefully explaining that i had provided all relevant information.
Jeff, before you response, did you read any of previous posts?
Sent from my iPhone
On Dec 27, 2011, at 6:19 PM, Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote:
> I suggest you (re-?)read the posting guide. Proper etiquette on this list is
> to provide a fully self-contained ("reproducible") example that demonstrates
> your problem. You are free to supply an alternate to your actual function as
> long as it illustrates your problem and you can deal with the re-substitution
> on your own.
> ---------------------------------------------------------------------------
> Jeff Newmiller The ..... ..... Go Live...
> DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go...
> Live: OO#.. Dead: OO#.. Playing
> Research Engineer (Solar/Batteries O.O#. #.O#. with
> /Software/Embedded Controllers) .OO#. .OO#. rocks...1k
> ---------------------------------------------------------------------------
> Sent from my phone. Please excuse my brevity.
>
> Alex Zhang <alex.zh...@ymail.com> wrote:
>
>> John,
>>
>> Thank you for your comment.�
>>
>> There is no secret. But the actual function I need to call is rather
>> irrelevant.�However don't take it as the "abs" function. If you like to
>> know, it is a function that converts 4 kinds of old ids from several
>> old database tables into a new id in a new database. Again, I don't
>> think providing�such detail is better than saying MyDummyFunc maps a
>> number into a number but doesn't work�with vectors.
>>
>> All I need to do, is to call DummyFunc for every element in a column of
>> a data.frame and returns�the resulted vector. But, I cannot change
>> DummyFunc. Correct me if I am wrong: this is rather�common in a
>> group�collaboration enviroment. Person A may be responsible for writing
>> a function and person B who needs to use that function cannot or better
>> not change it.
>>
>> Obviously, I could write a loop. Michael in a previous post suggested
>> using vectorize which works perfectly. As a newbie of R, I would wish
>> to learn more ways to achieve my goal (sorry, it automatically involves
>> "how" not just "what" ;). Is there a way using�a "*apply" function to
>> do it where * stands for any function.
>>
>> Thanks a lot!�
>>
>>
>> ________________________________
>> From: John Fox <j...@mcmaster.ca>
>> To: 'Alex Zhang' <alex.zh...@ymail.com>
>> Cc: r-help@r-project.org
>> Sent: Tuesday, December 27, 2011 4:06 PM
>> Subject: RE: [R] sapply Call Returning " the condition has length > 1"
>> Error
>>
>> Dear Alex,
>>
>>> -----Original Message-----
>>> From: Alex Zhang [mailto:alex.zh...@ymail.com]
>>> Sent: December-27-11 3:34 PM
>>> To: John Fox
>>> Cc: r-help@r-project.org
>>> Subject: Re: [R] sapply Call Returning " the condition has length >
>> 1"
>>> Error
>>>
>>> John,
>>>
>>> Thanks for the pointers.
>>>
>>> The DummyFunc is just a made-up example. The true function I need to
>>> use is more complicated and would be distractive to include.
>>
>> You'll probably get a better answer if you don't keep what you want to
>> do a
>> secret.
>>
>>>
>>> Do you mean that sapply would take columns in the input data.frame
>> and
>>> feed them into "FUN" as "whole" vectors? That explains the behavior.
>>
>> Yes. As I said, a data frame is a list of columns, so FUN is called
>> with
>> each column as its argument.
>>
>>> Is there an "*apply" function that will fee elements of the input
>>> data.frame into "FUN" instead of whole columns? Thanks.
>>
>> I'm afraid that I don't know what you mean. Do you want to deal with
>> the
>> columns of the data frame separately (in general, they need not all be
>> of
>> the same class), and within each column, apply a function separately to
>> each
>> element? You could nest calls to lapply() or sapply(), as in
>>
>> sapply(D, function(DD) sapply(DD, abs))
>>
>> assuming, of course, that D is an entirely numeric data frame. But in
>> this
>> case,
>>
>> abs(as.matrix(D))
>>
>> would be more sensible, and using sapply() like this isn't necessarily
>> better than a loop. Again, not knowing what you want to do makes it
>> hard to
>> suggest a solution.
>>
>> Best,
>> John
>>
>>>
>>> ________________________________
>>>
>>> From: John Fox <j...@mcmaster.ca>
>>> To: 'Alex Zhang' <alex.zh...@ymail.com>
>>> Cc: r-help@r-project.org
>>> Sent: Tuesday, December 27, 2011 3:10 PM
>>> Subject: RE: [R] sapply Call Returning " the condition has length >
>> 1"
>>> Error
>>>
>>> Dear Alex,
>>>
>>>> -----Original Message-----
>>>> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r-
>>>> project.org] On Behalf Of Alex Zhang
>>>> Sent: December-27-11 2:14 PM
>>>> To: r-help@r-project.org
>>>> Subject: [R] sapply Call Returning " the condition has length > 1"
>>>> Error
>>>>
>>>> Dear all,
>>>>
>>>> Happy new year!
>>>>
>>>> I have a question re using sapply. Below is a dummy example that
>>> would
>>>> replicate the error I saw.
>>>>
>>>> ##Code Starts here
>>>> DummyFunc <- function(x) {
>>>>
>>>> if (x > 0) {
>>>> return (x)
>>>> } else
>>>> {
>>>> return (-x)
>>>> }
>>>>
>>>> }
>>>>
>>>> Y = data.frame(val = c(-3:7))
>>>> sapply(Y, FUN = DummyFunc)
>>>> ##Code ends here
>>>>
>>>> When I run it, I got:
>>>> � � � val
>>>> � [1,]� 3
>>>> � [2,]� 2
>>>> � [3,]� 1
>>>> � [4,]� 0
>>>> � [5,]� -1
>>>> � [6,]� -2
>>>> � [7,]� -3
>>>> � [8,]� -4
>>>> � [9,]� -5
>>>> [10,]� -6
>>>> [11,]� -7
>>>> Warning message:
>>>> In if (x > 0) { :
>>>> � the condition has length > 1 and only the first element will be
>>> used
>>>>
>>>> The result is different from what I would expect plus there is such
>>> an
>>>> error message.
>>>
>>> This is a warning, not really an error message. A data frame is
>>> essentially a list of variables (columns), and sapply() applies its
>>> FUN argument to each list element, that is, each variable -- the one
>>> variable val in your case.
>>> That produces a warning because val > 0 is a vector of 11 elements,
>>> and the first comparison, 3 > 0, which is TRUE, controls the result.
>>>
>>>>
>>>> I guess if the DummyFunc I provided is compatible with vectors, the
>>>> problem would go away. But let's suppose I cannot change DummyFunc.
>>> Is
>>>> there still a way to use sapply or alike without actually writing a
>>>> loop? Thanks.
>>>
>>> Well, you could just use
>>>
>>>> abs(Y$val)
>>> [1] 3 2 1 0 1 2 3 4 5 6 7
>>>
>>> but I suppose that you didn't really want to write your own version
>> of
>>> the absolute-value function as something more than an exercise.
>>>
>>> An alternative is
>>>
>>>> with(Y, ifelse(val > 0, val, -val))
>>> [1] 3 2 1 0 1 2 3 4 5 6 7
>>>
>>> I hope this helps,
>>> John
>>>
>>> --------------------------------
>>> John Fox
>>> Senator William McMaster
>>> � Professor of Social Statistics
>>> Department of Sociology
>>> McMaster University
>>> Hamilton, Ontario, Canada
>>> http://socserv.mcmaster.ca/jfox
>>>
>>>
>>>
>>>>
>>>> - Alex
>>>> � � [[alternative HTML version deleted]]
>>>
>>>
>>>
>>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@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.
>
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