[R] Avoiding loops

[Phil Spector]

Another advantage of the apply family of functions is that
they determine the size and type of their output in an
efficient way, which is sometimes tricky when you write 
the loop yourself.

                                         - Phil Spector
                                          Statistical Computing Facility
                                          Department of Statistics
                                          UC Berkeley
                                          spector at stat.berkeley.edu


On Wed, 2 Sep 2009, Alexander Shenkin wrote:

> Though, from my limited understanding, the 'apply' family of functions
> are actually just loops.  Please correct me if I'm wrong.  So, while
> more readable (which is important), they're not necessarily more
> efficient than explicit 'for' loops.
>
> allie
>
> On 9/2/2009 3:13 AM, Phil Spector wrote:
>> Here's one way (assuming your data frame is named dat):
>>
>>    with(dat,
>>         data.frame(a,t(sapply(a,function(x){
>>                        apply(dat[a - x >= -5 & a - x <=
>> 0,c('b','c')],2,sum)}))))
>>
>>
>>                     - Phil Spector
>>                      Statistical Computing Facility
>>                      Department of Statistics
>>                      UC Berkeley
>>                      spector at stat.berkeley.edu
>>
>>
>>
>> On Tue, 1 Sep 2009, dolar wrote:
>>
>>>
>>> Would like some tips on how to avoid loops as I know they are slow in R
>>>
>>> i've got a data frame :
>>>
>>> a  b  c
>>> 1  5  2
>>> 4  6  9
>>> 5  2  3
>>> 8  3  2
>>>
>>> What i'd like is to sum for each value of a, the sum of b and the sum
>>> of c
>>> where a equal to or less than (with a distance of 5)
>>>
>>> i.e. for row three
>>> we have a=5
>>> i'd like to sum up b and sum up c with the above rule
>>> since 5, 4 and 1 are less than (within a distance of 5) or equal to
>>> 5, then
>>> we should get the following result:
>>>
>>> a  b   c
>>> 5  13  14
>>>
>>> the overall result should be
>>> a   b   c
>>> 1   5   2
>>> 4   11  11
>>> 5   13  14
>>> 8   11  14
>>>
>>> how can i do this without a loop?
>>> --
>>> View this message in context:
>>> http://www.nabble.com/Avoiding-loops-tp25251376p25251376.html
>>> Sent from the R help mailing list archive at Nabble.com.
>>>
>>> ______________________________________________
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>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>> ______________________________________________
>> 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.
>
> ______________________________________________
> 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.
>