# [R] simplify code for dummy coding of factors

Michael Friendly friendly at yorku.ca
Wed Dec 31 00:05:04 CET 2014

```In a manuscript, I have the following code to illustrate dummy coding of
two factors in a contingency table.

It works, but is surely obscured by the method I used, involving outer()
to find equalities and 0+outer()
to convert to numeric.  Can someone help simplify this code to be more
comprehensible and give the
*same* result? I'd prefer a solution that uses base R.

haireye <- margin.table(HairEyeColor, 1:2)

haireye.df <- as.data.frame(haireye)
dummy.hair <-  0+outer(haireye.df\$Hair, levels(haireye.df\$Hair), `==`)
colnames(dummy.hair)  <- paste0('h', 1:4)
dummy.eye <-  0+outer(haireye.df\$Eye, levels(haireye.df\$Eye), `==`)
colnames(dummy.eye)  <- paste0('e', 1:4)

haireye.df <- data.frame(haireye.df, dummy.hair, dummy.eye)
haireye.df

> haireye.df
Hair   Eye Freq h1 h2 h3 h4 e1 e2 e3 e4
1  Black Brown   68  1  0  0  0  1  0  0  0
2  Brown Brown  119  0  1  0  0  1  0  0  0
3    Red Brown   26  0  0  1  0  1  0  0  0
4  Blond Brown    7  0  0  0  1  1  0  0  0
5  Black  Blue   20  1  0  0  0  0  1  0  0
6  Brown  Blue   84  0  1  0  0  0  1  0  0
7    Red  Blue   17  0  0  1  0  0  1  0  0
8  Blond  Blue   94  0  0  0  1  0  1  0  0
9  Black Hazel   15  1  0  0  0  0  0  1  0
10 Brown Hazel   54  0  1  0  0  0  0  1  0
11   Red Hazel   14  0  0  1  0  0  0  1  0
12 Blond Hazel   10  0  0  0  1  0  0  1  0
13 Black Green    5  1  0  0  0  0  0  0  1
14 Brown Green   29  0  1  0  0  0  0  0  1
15   Red Green   14  0  0  1  0  0  0  0  1
16 Blond Green   16  0  0  0  1  0  0  0  1
>

--
Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University      Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street    Web:http://www.datavis.ca