R-alpha: NA in data frame not detected

[Friedrich Leisch]

NA's in a data frame are not handled properly, if the data frame was
read in using read.table (but I'm not sure if that is the reason of
the problems):

(I'm using Debian Linux 1.3)

If I read the file

***************
1 2
2 3
3 4
4 5
? 6
6 7
7 8
8 9
***************

into R using read.table I run into troubles:

R : Copyright 1997, Robert Gentleman and Ross Ihaka
Version 0.49 Beta (April 23, 1997)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type "license()" for details.

R> x<-read.table("xxx", na.strings=3D"?")
R> x
  V1 V2
1  1  2
2  2  3
3  3  4
4  4  5
5 NA  6
6  6  7
7  7  8
8  8  9
R> complete.cases(x)
[1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE
R> x$V1
[1]  1  2  3  4 NA  6  7  8
R> x$V1[5]
[1] NA
R> is.na(x$V1[5])
[1] FALSE


but if I create the same dataframe in R I get the expected results:

R> z<-data.frame(V1=3Dc(1:4, NA, 6:8), y2=3D2:9)
R> z
     V1 y2
[1,]  1  2
[2,]  2  3
[3,]  3  4
[4,]  4  5
[5,] NA  6
[6,]  6  7
[7,]  7  8
[8,]  8  9
R> complete.cases(z)
[1]  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE  TRUE
R> is.na(z$V1[5])
[1] TRUE




Can anybody confirm this?

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                        Friedrich  Leisch                            =20
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