On Apr 10, 2012, at 11:58 AM, Rainer Schuermann wrote:
cbind() works as well, but only if c is attached to the existing
test variable:
tst <- cbind( test, c )
tst
a b c
1 1 0.3 y1
2 2 0.4 y2
3 3 0.5 y3
4 4 0.6 y4
5 5 0.7 y5
str( tst )
'data.frame': 5 obs. of 3 variables:
$ a: num 1 2 3 4 5
$ b: num 0.3 0.4 0.5 0.6 0.7
$ c: Factor w/ 5 levels "y1","y2","y3",..: 1 2 3 4 5
Not saying it is a good idea, though...
To be somewhat more expansive ... 'cbind' is not just one function,
but rather a set of functions, since it is "generic". The one that is
chosen by the interpreter will depend on whether the first argument
has a class. If it does have a class as in the example above having a
class of "data.frame", then the cbind.data.frame function will be
dispatched to process the list of arguments. If the first argument
doesn't have a class as in the OP's second example below, then the
internal cbind function will be used and returns a matrics which
strips off all but a few attributes and forces a lowest common
denominator mode. If only one of the arguments were logical, then
cbind would return a a matrix of all TRUEs and FALSEs.
(This all assumes that the typos in the OP's original example that
created 'c' as an incomplete expression and a and b with unequal
lengths were fixed.)
> a <- c(1,2,3,4,5);
> b <- c(0.3,0.4,0.5,0,6,0.7);
> test <- data.frame(cbind(a,b))
Warning message:
In cbind(a, b) :
number of rows of result is not a multiple of vector length (arg 1)
> c <- c("y1","y2","y3","y4","y5")
> cbind(c, test)
Error in data.frame(..., check.names = FALSE) :
arguments imply differing number of rows: 5, 6
--
David.
Rainer
On Tuesday 10 April 2012 11:38:51 R. Michael Weylandt wrote:
Don't use cbind() -- it forces everything into a single type, here
string, which in turn becomes factor.
Simply,
data.frame(a, b, c)
Like David mentioned a few days ago, I have no idea who is promoting
this data.frame(cbind(...)) idiom, but it's a terrible idea (albeit
one that seems to be very frequent over the last few weeks)
Michael
On Tue, Apr 10, 2012 at 10:33 AM, Anser Chen <anser.c...@gmail.com>
wrote:
Complete newbie to R -- struggling with something which should be
pretty
basic. Trying to create a simple data set (which I gather R refers
to as a
data.frame). So
a <- c(1,2,3,4,5);
b <- c(0.3,0.4,0.5,0,6,0.7);
Stick the two together into a data frame (call test) using cbind
test <- data.frame(cbind(a,b))
Seems to do the trick:
test
a b
1 1 0.3
2 2 0.4
3 3 0.5
4 4 0.6
5 5 0.7
Confirm that each variable is numeric:
is.numeric(test$a)
[1] TRUE
is.numeric(test$b)
[1] TRUE
OK, so far so good. But, now I want to merge in a vector of
characters:
c <- c('y1","y2","y3","y4","y5")
Confirm that this is string:
is.numeric(c);
[1] FALSE
cbind c into the data frame:
test <- data.frame(cbind(a,b,c))
Looks like everything is in place:
test
a b c
1 1 0.3 y1
2 2 0.4 y2
3 3 0.5 y3
4 4 0.6 y4
5 5 0.7 y5
Except that it seems as if the moment I cbind in a character
vector, it
changes numeric data to string:
is.numeric(test$a)
[1] FALSE
is.numeric(test$b)
[1] FALSE
which would explain why the operations I'm trying to perform on
elements of
a and b columns are failing. If I look at the structure of the
data.frame,
I see that in fact *all* the variables are being entered as
"factors".
str(test)
'data.frame': 5 obs. of 3 variables:
$ a: Factor w/ 5 levels "1","2","3","4",..: 1 2 3 4 5
$ b: Factor w/ 5 levels "0.3","0.4","0.5",..: 1 2 3 4 5
$ c: Factor w/ 5 levels "y1","y2","y3",..: 1 2 3 4 5
But, if I try
test <- data.frame(cbind(a,b))
str(test)
'data.frame': 5 obs. of 2 variables:
$ a: num 1 2 3 4 5
$ b: num 0.3 0.4 0.5 0.6 0.7
a and b are coming back as numeric. So, why does cbind'ing a
column of
character variables change everything else? And, more to the
point, what do
I need to do to 'correct' the problem (i.e., stop this from
happening).
[[alternative HTML version deleted]]
David Winsemius, MD
West Hartford, CT
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