Re: [R] Creating Binary Outcomes from a continuous variable

[Douglas Bates]

Marc Schwartz wrote:
On Wed, 2004-07-07 at 07:57, Doran, Harold wrote:
Dear List:
I have searched the archives and my R books and cannot find a method to
transform a continuous variable into a binary variable. For example, I
have test score data along a continuous scale. I want to create a new
variable in my dataset that is 1=above a cutpoint (or passed the test)
and 0=otherwise.

My instinct tells me that this will require a combination of the
transform command along with a conditional selection. Any help is much
appreciated.

Example:

a <- rnorm(20)
b <- ifelse(a < 0, 0, 1)

a
 [1] -1.0735800 -0.6788456  1.9979801 -0.4026760  0.1781791 -1.1540434
 [7] -1.0842728  1.6042602 -0.7950492 -0.1194323  0.4450296  1.9269333
[13] -0.4456181 -0.8374677 -1.1898772  1.7353067  1.8619422 -0.1679996
[19] -0.2656138 -1.5529884
b
 [1] 0 0 1 0 1 0 0 1 0 0 1 1 0 0 0 1 1 0 0 0
HTH,
Marc Schwartz
For your application Harold I would consider converting the response to 
a factor while dichotomizing it so that summary will give a meaningful table

b <- factor(ifelse(a < 0, "Neg", "Pos"))
BTW, there are many examples like this in the notes for the short course 
that you took last summer  :-)

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