adding logical vector to data frame

Hello.  I'm afraid that I'm missing something very obvious this
afternoon...

When I add a column to a data.frame (by assigning to a "new" column
name a logical vector), I thought that I had (at least) 3 options to
do so:

R> j <- data.frame (x=1:2)

R> j$y <- c(TRUE,FALSE) #assignment 1
R> str(j)
`data.frame':	2 obs. of  2 variables:
$ x: int  1 2
$ y: logi   TRUE FALSE

R> j[["y"]] <- c(TRUE,FALSE) #assignment 2
R> str(j)
`data.frame':	2 obs. of  2 variables:
$ x: int  1 2
$ y: Factor w/ 2 levels "FALSE","TRUE": 2 1

R> j[["y"]] <- I(c(TRUE,FALSE)) #assignment 3
R> str(j)
`data.frame':	2 obs. of  2 variables:
$ x: int  1 2
$ y:Class 'AsIs'  logi [1:2]  TRUE FALSE


Why is assignment 1 not identical to either assignment 2 or 3?  Is
there a method dispatch skipped?

Thanks!
 -tom

Hi,

I think that if you use names for indexing, you have to use single brackets
["..."], not double as in your example:

j <- data.frame (x=1:2)
j["y"] <- c(TRUE,FALSE) #assignment 4
str(j)

`data.frame':   2 obs. of  2 variables:
 $ x: int  1 2
 $ y: logi   TRUE FALSE


You'll need a more expert opinion than mine to explain the differences
between [ and [[, but look at the following:

x <- 1:9
names(x) <- LETTERS[x] # give names to the observations
x

A B C D E F G H I 
1 2 3 4 5 6 7 8 9

x["C"]

C 
3

x[["C"]]

[1] 3

names(x["C"])

[1] "C"

names(x[["C"]])

NULL

The same with numeric indexing, but not logical indexing:

x[3]

C 
3

x[[3]]

[1] 3

x[x == 3]

C 
3

x[[x == 3]]

Error: attempt to select more than one element



Emmanuel Paradis
Laboratoire de Pal?ontologie
Institut des Sciences de l'?volution
Universit? Montpellier II
F-34095 Montpellier c?dex 05
France
   phone: +33  4 67 14 39 64
     fax: +33  4 67 14 36 10
  mailto:paradis at isem.univ-montp2.fr
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