I used read.dta() to read in a Stata 9 dataset to R. The "Sex01" variable
takes on two values in Stata: 0 and 1, and it is labeled "M" and "F"
respectively, analogous to an R factor. Thus, read.dta reads it in as a
factor.

Now, I wanted to see what this variable *really* is, in R. For instance,
sometimes R converts a 0/1 variable into a 1/2 variable when it considers it
a factor. The "dput" function often enables me to see what a variable really
is, but in this case it tells me that the components of the factor are "1L"
and "2L", that is, "one uppercase ell" and "two uppercase ell."  What does
the uppercase ell mean?

In this case, "unclass" seems to enable me to see what the variable really
consists of. But what do "1L" and "2L" mean?

> summary(DAT$Sex01[1:150])
  M   F
137  13
> dput(DAT$Sex01[1:150])
structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L,
1L, 2L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L,
2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L,
2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("M", "F"), class = "factor")

> unclass(junk)
  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 2 1 1 2 2 1 1 1 1 1 2 2 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 1 1 1 1 1
[149] 1 1
attr(,"levels")
[1] "M" "F"

> str(junk)
 Factor w/ 2 levels "M","F": 1 1 1 1 1 1 1 1 1 1 ...


Jake

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