Re: [R] Help with which()

From: Ted Harding <Ted.Harding_at_manchester.ac.uk>
Date: Thu, 24 Jul 2008 17:33:33 +0100 (BST)


On 24-Jul-08 15:35:45, Erik Iverson wrote:

> See
> 
> http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-the
> se-numbers-are-equal_003f

That's not an applicable response: The difference between 3573.1 and 3573.15 is far too large for them to be confused by "==". Thr confusion only sets in at a difference of around 1e-15. In any case, test it for yourself:

  3573.1==3573.15
# [1] FALSE The only explanations I can think of are on the lines of a) Nina thinks that the second position holds 3573.15, but it

   really holds 3573.1 and Nina was mistaken about the position.

b) For some reason, a number in Operons which has been entered

   as, and reads on screen as, 3573.15 is being read as 3573.1    by R. I have no idea how that could happen, but it might be    possible if a stray byte (not visible on screen) has crept    in between the "1" and the "5": 3573.1?5

I think the first thing is that Nina should check the contents of Operons very carefully.

What is the result of

  Operons[which(Operons==3573.1,arr.ind=TRUE)]

??

Ted.

> naw3_at_duke.edu wrote:

>> Hi,
>>
>> I'm using which to find the position of a value in my data table,
>> and it is returning the correct position and the position of
>> another number that differs by an extra decimal place. For example,
>> when I do:
>>
>> where1<-which(Operons==3573.1,arr.ind=TRUE)
>>
>> it returns the position of that number and of 3573.15.
>>
>> Is it possible to get the function to only return a position if
>> the number matches exactly?
>>
>> Thanks,
>> -Nina
>>
>> ______________________________________________
>> 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.

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Date: 24-Jul-08                                       Time: 17:33:26
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