[R] how to use vectorization instead of for loop

[ruipbarradas at sapo.pt]

Hello,

Use combined ifelses, more or less like the following.

ifelse(dat[, 2] == Inf, do this, ifelse(dat[, 2] > 0, 1 * (1/dat[,3]),  
-1* (1/dat[,3])))

Rui Barradas
 

Citando Stephen HK WONG <honkit at stanford.edu>:

> So much thanks Rui, the code can be so simple and fast.
>
> By the way, ifelse is good for two conditions, in my case, either  
> >0, or <0, I found there's a lot of row with value "Inf", I want to  
> keep it in new column, how do I do that using ifelse ?
>
> Thanks.
>
> ________________________________________
> From: ruipbarradas at sapo.pt <ruipbarradas at sapo.pt>
> Sent: Monday, March 21, 2016 11:50 AM
> To: Stephen HK WONG
> Cc: r-help at r-project.org
> Subject: Re: [R] how to use vectorization instead of for loop
>
> Hello,
>
> I've renamed your dataframe to 'dat'. Since ?ifelse is vectorized, try
>
> dat[, 4] <- ifelse(dat[, 2] > 0, 1 * (1/dat[,3]), -1* (1/dat[,3]))
>
> Oh, and why do you multiply by 1 and by -1?
> It would simply be 1/dat[,3] and -1/dat[,3].
>
> Hope this helps,
>
> Rui Barradas
>
> Quoting Stephen HK WONG <honkit at stanford.edu>:
>> Dear All,
>>
>> I have a dataframe like below but with many thousands rows,
>>
>> structure(list(gene_id = structure(1:6, .Label = c("0610005C13Rik",
>> "0610007P14Rik", "0610009B22Rik", "0610009L18Rik", "0610009O20Rik",
>> "0610010B08Rik,OTTMUSG00000016609"), class = "factor"),
>> log2.fold_change. = c(0.0114463,
>> -0.0960262, 0.00805151, -0.179981, -0.0629098, 0.155979), p_value = c(1,
>> 0.77915, 0.98265, 0.68665, 0.85035, 0.72235), new.value = c("NA",
>> "NA", "NA", "NA", "NA", "NA")), .Names = c("gene_id", "log2.fold_change.",
>> "p_value", "new.value"), row.names = c(NA, 6L), class = "data.frame")
>>
>> I want to check if second column is positive or negative value, then
>> I will do some calculation and put the new value in last column. I
>> can do this with for loop like below but it is not efficient. Is
>> there a better way to use a vectorization method instead of loop?
>> Many thanks!
>>
>> for (i in 1:nrow(dataframe)) {
>>
>> if dataframe[i, 2]>0 {
>>
>> dataframe[i, 4]<- 1 * (1/dataframe[i,3])} else{
>>
>> dataframe[i, 4] <- -1* (1/dataframe[i,3])}
>>
>> }
>>
>> -------------------------------------------------------
>>
>> Stephen H.K. WONG, PhD.
>>
>> Stanford University
>>
>>       [[alternative HTML version deleted]]
>>
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>> PLEASE do read the posting guide  
>> http://www.R-project.org/posting-guide.htmland provide commented,  
>> minimal, self-contained, reproducible code.
>
>  

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