Re: [R] logical condition in vector operation

From: Christoph Buser <buser_at_stat.math.ethz.ch>
Date: Thu 09 Feb 2006 - 19:22:30 EST

Dear Frederico

>From your example it is not clear to me what you like to obtain: Please have a look on the slightly changed example here (I changed two values to show a potentially undesired side effect of your coding.

test <- data.frame(rbind(c(3,3,10,21,0), c(2,3,11,12,0), c(3,4,12,23,0),
                         c(3,5,13,24,0)))
names(test) <- c("x","y","p","d","su")

test
>>   x y  p  d su
>> 1 3 3 10 21  0
>> 2 2 3 11 12  0
>> 3 3 4 12 23  0
>> 4 3 5 13 24  0

j <- 3
test[test[,1] == j, 5] <- test[test[,1] == j,2] + test[test[,2] == j,1]

>> > > Warning message:
>> longer object length
>> 	is not a multiple of shorter object length in: 
>>         test[test[, 1] == j, 2] + test[test[, 2] == j, 1] 

Your code example produces now a warning for the adapted data frame "test", since one tries to add two vectors of length 2 and 3, respectively. The result is based on recycling of the smaller vector. In your example there was no warning since the second column had only one entry.
The result with the adapted data frame is:

test

>>   x y  p  d su
>> 1 3 3 10 21  6
>> 2 2 3 11 12  0
>> 3 3 4 12 23  6
>> 4 3 5 13 24  8

Is that kind of recycling desired in your application. Otherwise you should be careful with the coding example above.

Regards,

Christoph Buser



Christoph Buser <buser@stat.math.ethz.ch> Seminar fuer Statistik, LEO C13
ETH (Federal Inst. Technology)	8092 Zurich	 SWITZERLAND
phone: x-41-44-632-4673		fax: 632-1228

http://stat.ethz.ch/~buser/

Federico Calboli writes:
> HI All,
>
> I have a data frame such as:
>
> > test
> x y p d
> [1,] 1 0 10 21 0
> [2,] 2 3 11 12 0
> [3,] 3 4 12 23 0
> [4,] 3 5 13 24 0
>
>
> and I want to perfor some operations on the first two coulums,
> conditional on the uneqaulity values on the 3rd and 4th columns.
>
> For instance:
>
> j = 3
> test[test[,1] == j, 5] = test[test[,1] == j,2] + test[test[,2] == j,1]
>
> gives me the result:
>
> test:
>
> x y p d
> [1,] 1 0 10 21 0
> [2,] 2 3 11 12 0
> [3,] 3 4 12 23 6
> [4,] 3 5 13 24 7
>
>
> My probblem is the following: I want to perform the operation
> test[test[,1] == j,2] + test[test[,2] == j,1] only if the value of
> column p and column d are different at the positions where x or y = j.
> In practice, I don't want to perform the first operation because
> test[2,4 is 12 and test[1,3] is 12 as well.
>
> I tried an if statement with little success:
>
> if(test[test[,1] == j,3] != test[test[,2] == j,4]){
> test[test[,1] == j, 5] = test[test[,1] == j,2] + test[test[,2] == j,1]
> }
> Warning message:
> the condition has length > 1 and only the first element will be used in:
> if (test[test[, 1] == j, 3] != test[test[, 2] == j, 4]) {
>
> Could anyone lend some advice?
>
> Cheers,
>
> Federico
> --
> Federico C. F. Calboli
> Department of Epidemiology and Public Health
> Imperial College, St Mary's Campus
> Norfolk Place, London W2 1PG
>
> Tel +44 (0)20 7594 1602 Fax (+44) 020 7594 3193
>
> f.calboli [.a.t] imperial.ac.uk
> f.calboli [.a.t] gmail.com
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Feb 09 23:30:54 2006

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