[R] Creating factors from continuous variables

From: David James <djames_at_frontierassoc.com>
Date: Sat 27 Aug 2005 - 06:59:45 EST


What is the quickest way to create many categorical variables (factors) from continuous variables?

This is the approach that I have used:

# create sample data

N <- 20
x <- runif(N,0,1)

# setup ranges to define categories

x.a <- (x >= 0.0) & (x < 0.4)
x.b <- (x >= 0.4) & (x < 0.5)
x.c <- (x >= 0.5) & (x < 0.6)
x.d <- (x >= 0.6) & (x < 1.0)

# create factors

i <- runif(N,1,1)
x.new <- (i*1*x.a) + (i*2*x.b) + (i*3*x.c) + (i*4*x.d) x.factor <- factor(x.new)

I'm looking for a better / simpler / more elegant / more robust (as the number of categories increases) way to do this. I also don't like that my factor names can only be numbers in this example. I would prefer a solution to take a form like the following (inspired by the "hist" function):

# define breakpoints

x.breaks = c(0, 0.4, 0.5, 0.6, 1.0)
x.factornames = c( "0 - 0.4", "0.4 - 0.5", "0.5 - 0.6", "0.6 - 1.0" )
x.factor = unknown.function( x, x.breaks, x.factornames )

Thanks,
David

P.S. Here's what I have read to try to find the answer to my problem:

* "Introductory Statistics with R"
* "A Brief Guide to R for Beginners in Econometrics"
* "Econometrics in R"

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