CategoricalVariables

d <- data.frame(ResState=c('CA', 'NV', 'OR', 'CA', 'CA', NA, 'WA', 'OR', 'WA'))
print(d)

##   ResState
## 1       CA
## 2       NV
## 3       OR
## 4       CA
## 5       CA
## 6     <NA>
## 7       WA
## 8       OR
## 9       WA

print(model.matrix(~ResState,data=d))

##   (Intercept) ResStateNV ResStateOR ResStateWA
## 1           1          0          0          0
## 2           1          1          0          0
## 3           1          0          1          0
## 4           1          0          0          0
## 5           1          0          0          0
## 7           1          0          0          1
## 8           1          0          1          0
## 9           1          0          0          1
## attr(,"assign")
## [1] 0 1 1 1
## attr(,"contrasts")
## attr(,"contrasts")$ResState
## [1] "contr.treatment"

# row 6 missing!

d$ResState <- addNA(d$ResState,ifany=TRUE)
print(model.matrix(~ResState,data=d))

##   (Intercept) ResStateNV ResStateOR ResStateWA ResStateNA
## 1           1          0          0          0          0
## 2           1          1          0          0          0
## 3           1          0          1          0          0
## 4           1          0          0          0          0
## 5           1          0          0          0          0
## 6           1          0          0          0          1
## 7           1          0          0          1          0
## 8           1          0          1          0          0
## 9           1          0          0          1          0
## attr(,"assign")
## [1] 0 1 1 1 1
## attr(,"contrasts")
## attr(,"contrasts")$ResState
## [1] "contr.treatment"

print(model.matrix(~0+ResState,data=d))

##   ResStateCA ResStateNV ResStateOR ResStateWA ResStateNA
## 1          1          0          0          0          0
## 2          0          1          0          0          0
## 3          0          0          1          0          0
## 4          1          0          0          0          0
## 5          1          0          0          0          0
## 6          0          0          0          0          1
## 7          0          0          0          1          0
## 8          0          0          1          0          0
## 9          0          0          0          1          0
## attr(,"assign")
## [1] 1 1 1 1 1
## attr(,"contrasts")
## attr(,"contrasts")$ResState
## [1] "contr.treatment"

# two incompatible factors
f1 <- factor(c("a","b","c"))
print(f1)

## [1] a b c
## Levels: a b c

print(as.numeric(f1))

## [1] 1 2 3

print(attr(f1,'levels'))

## [1] "a" "b" "c"

f2 <- factor(c("a","b","c"),levels=c("c","b","a"))
print(f2)

## [1] a b c
## Levels: c b a

print(as.numeric(f2))

## [1] 3 2 1