[R] replace a for loop

[Ivan Calandra]

Well actually, in that case, I don't think it is really necessary to 
replace the loop because it is quite fast with the small size I have. 
But I thought it would help me to understand how would vectorization 
work and how to use the *apply functions.
Thanks anyway for your piece of advice!
Ivan

Le 2/10/2010 17:03, Petr PIKAL a écrit :
> Hi
>
> how many objects do you have in a list? Loop is ineffective if you use
> several nested loops and/or there is some unnecessary mimic of simple
> function.
>
> e.g. you can use this
>
> set.seed(666)
> x<- runif(10)
> vysled<- 0
> for(i in 1:length(x)) {
> if(vysled>  x[i]) vysled<- vysled else vysled<- x[i]
> }
> vysled
>
> but I would prefer max(x)
>
> If you do not perceive performance issues there is usually no need to
> elaborate *apply.
>
> Regards
> Petr
>
>
>
> r-help-bounces at r-project.org napsal dne 10.02.2010 11:59:21:
>
>    
>> After reading the R news, I've tried this code and it works:
>>   >  rapply(list(names(test),test), write.csv, file="filename.csv",
>> append=T, row.names=F)
>>
>> However, the output is structured like this:
>> names(test)[[1]]
>> names(test)[[2]]
>> etc...
>> test[[1]]
>> test[[2]]
>> etc...
>>
>> I would like to alternate names(test) and test in the output. The
>> desired output would be structured like this:
>> names(test)[[1]]
>> test[[1]]
>> names(test)[[2]]
>> test[[2]]
>> etc...
>>
>> Can someone guide me for that step? Better solutions for the whole thing
>>      
>    
>> are of course welcomed!
>>
>> Thanks a lot
>> Ivan
>>
>> Le 2/10/2010 10:50, Ivan Calandra a écrit :
>>      
>>> Hi everybody!
>>>
>>> I'm still quite new in R and I don't really understand this whole
>>> "vectorization" thing.
>>> For now, I use a for loop (and it works fine), but I think it would be
>>>        
>    
>>> useful to replace it.
>>>
>>> I want to export the result of a test statistic, which is stored as a
>>> list, into a csv file. I therefore have to export each element of the
>>> list separately.
>>> Here is the code:
>>> ----
>>> str(test)
>>> List of 3
>>>   $ output : num [1:15, 1:6] 1 2 3 4 5 6 7 8 9 10 ...
>>>    ..- attr(*, "dimnames")=List of 2
>>>    .. ..$ : NULL
>>>    .. ..$ : chr [1:6] "con.num" "psihat" "p.value" "p.crit" ...
>>>   $ con    : num [1:6, 1:15] 1 -1 0 0 0 0 1 0 -1 0 ...
>>>   $ num.sig: int 0
>>>
>>> for (i in 1:3){
>>>   write.csv(test[[i]], file="filename.csv", append=T, quote=F,
>>> row.names=T)
>>> }
>>> ----
>>>
>>> As I said, I don't completely understand, but I think one of these
>>> "apply" function might do what I need.
>>>
>>> Thanks in advance
>>> Ivan
>>>
>>> ______________________________________________
>>> 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.
>>      
>
>