On 3/04/2009, at 9:30 AM, gina patel wrote:
I have created this data frame to help illustrate my problem.
id<-c(rep(1,5),rep(2,5),rep(3,5),rep(4,5),rep(5,5))
x<-rep((seq(1:5)),5)
y<-c(0, 0.1, 0.5, 0.4, 0.2, 0, 0.1, 0.5, 0.4, 0.12, 0, 0.1, 0.5,
0.55, 0.2, 0, 0.1, 0.5, 0.3, 0.2, 0, 0.1, 0.6, 0.4, 0.1)
d1<-cbind(id,x,y)
I would like to delete all rows where id=4, however, when I tried
the command
d2=d1[-c(id==4),]
and looked at d2 no data was removed.
Thanks in advance, I appreciate any help.
Others have told you how to do what you want. It would be useful
for you to understand why what you ***did*** didn't work.
Note that ``id==4'' yields a *logical* vector with entries TRUE and
FALSE.
When an arithmetic operator is applied, as in -(id==4) [NOTE: THE ``c
()'' wrapper
is TOTALLY UNNECESSARY HERE.] the vector is coerced to a numeric
vector of
-1's (for TRUE) and 0's (for FALSE). Thus you are asking d2 to be d1
[i,] where
i is a vector of -1's and 0's. The -1's say to throw away the ``1-
th'' (first)
row of d1; the 0's say to pick out the 0-th row of d1 (and there is
no 0-th row
so this doesn't do anything). Thus you are in effect asking for d1
[2:25,].
And that's what you get. Look carefully --- it is not correct to say
that when
you looked at d2 *no* data were removed; d2 is equal to d1 with its
first row
removed. I.e. your operation didn't remove what you wanted, but it
removed
*something*.
cheers,
Rolf Turner
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