[R] Count factor if

[Dimitris Rizopoulos]

try this:

x <- factor(c('a','a','a','a','a','b','b','b','c','d','d','d'))
y <- c(1,3,6,8,8,3,4,7,5,6,7,10)
X <- data.frame(x, y)

cbind(X, z = ave(X$y, X$x,
     FUN = function (x) match(x, unique(x)) - 1))


I hope it helps.

Best,
Dimitris


On 2/17/2011 11:15 AM, mathijsdevaan wrote:
>
>> Here is a method that works despite generating a warning:
>> cbind(X, z = ave(X$y, X$x, FUN = seq) - 1)
>>
>> David Winsemius, MD
>> West Hartford, CT
>
> I was happy a bit too early. There's still an error:
>
> x<-as.factor(c('a','a','a','a','a','b','b','b','c','d','d','d'))
> y<-c(1,3,6,8,8,3,4,7,5,6,7,10)
> X<-data.frame(x,y)
> X
>     x  y
> 1  a  1
> 2  a  3
> 3  a  6
> 4  a  8
> 5  a  8
> 6  b  3
> 7  b  4
> 8  b  7
> 9  c  5
> 10 d  6
> 11 d  7
> 12 d 10
>
> cbind(X, z = ave(X$y, X$x, FUN = seq) - 1)
>
>     x  y z
> 1  a  1 0
> 2  a  3 1
> 3  a  6 2
> 4  a  8 3
> 5  a  8 4
> 6  b  3 0
> 7  b  4 1
> 8  b  7 2
> 9  c  5 0
> 10 d  6 0
> 11 d  7 1
> 12 d 10 2
>
> Using this function provides a value of 4 in row 5, column c, while it
> should be 3. Is there another way I can solve my problem? Thanks!
>
> M

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
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