create new variable: percentile value of variable in data frame

Hello all,

Thanks in advance for you attention.
I would like to generate a third value that represents the quantile
value of a variable in a data frame.


# generating data

x <- as.matrix(seq(1:30))
y <- as.matrix(rnorm(30, 20, 7))
tmp1 <- cbind(x,y)
dat <- as.data.frame(tmp1)
colnames(dat) <- c("id", "score")
dat

#  finding percentiles of "score"

qs <- as.matrix(quantile(dat$score, type=3, probs = seq(0,1,.1)))
colnames(qs) <- c( "score")
qs

#  is there a way to put the quantile value for a value of 'score'
into a new variable,
#  such that the new data frame would have three variables: id, score
and q.score?

##  running R version 2.8.1 (2008-12-22) on Vista


Thanks so much!

-Jon

Hi Jon,

does the empirical cumulative distribution function do what you want?

dat$q.score <- ecdf(dat$score)(dat$score)
?ecdf

HTH
Stephan


Jonathan Beard schrieb:

Hello all,

Thanks in advance for you attention.
I would like to generate a third value that represents the quantile
value of a variable in a data frame.


# generating data

x <- as.matrix(seq(1:30))
y <- as.matrix(rnorm(30, 20, 7))
tmp1 <- cbind(x,y)
dat <- as.data.frame(tmp1)
colnames(dat) <- c("id", "score")
dat

# ?finding percentiles of "score"

qs <- as.matrix(quantile(dat$score, type=3, probs = seq(0,1,.1)))
colnames(qs) <- c( "score")
qs

# ?is there a way to put the quantile value for a value of 'score'
into a new variable,
# ?such that the new data frame would have three variables: id, score
and q.score?

## ?running R version 2.8.1 (2008-12-22) on Vista


Thanks so much!

-Jon

Hi Stephan, thanks for your response.

It looks like the ecdf() works like it should.

I have a quick follow-up:

I didn't notice any discussion in the help documents of the methods
behind ecdf() and quantile(type=3) being equivalent.

It looks like the results produced by each method are consistent.