On Apr 24, 2009, at 7:50 AM, onyourmark wrote:
Hi. Thanks very much for the reply and the good suggestion. It works
well.
But I don't get why the for loop is not deleting anything or making
any
assignments? Or I should say, doesn't answer3[-i,] delete entries from
answer3 when the if condition is true?
No, it doesn't. It returns a copy of answer3 without the ith row, but
it does not touch answer3, because as Ben said before you did no
assignment.
Also, in your first solution
answer2[-(answer2[,1]==answer2[,2]),]
can I say that you are indexing answer2 by answer2[,] and all of the
deletion is coming in the first argument and specifically you are
deleting
every entry in answer2 where the first elements of the first and
second
columns are the same.
Actually you are still not deleting. But the rest of you
characterization of the process looks correct.
So for example,
if I wanted instead to switch the elements of the first and second
column
whenever they are different what would I do? confused.
The easiest approach would probably be to swap their names but if you
want to swap the entries without touching the names then something like:
temp.ans <- answer2[,2]
answer2[ , 2] <- answer2[ , 1]
answer2[ , 2] <- temp.ans
Or possibly answer2[ , c(2,1)] <- answer2[ , c(1,2)] but I am not a
sufficiently experienced R programmer to know the answer to that
without testing.
--
David.
Ben Bolker wrote:
onyourmark wrote:
I have an object. I think it is a matrix, called 'answer2'
str(answer2)
int [1:1537, 1:2] 1 399 653 2 3 600 4 5 271 870 ...
- attr(*, "dimnames")=List of 2
..$ : chr [1:1537] "a4.1" "hirschsprung.399" "peritoneal.653"
"abdomen.2" ...
..$ : chr [1:2] "row" "col"
I want to delete rows that have the same entries.
Your "for" loop didn't make any assignments.
How about
answer3 <- answer2[-(answer2[,1]==answer2[,2]),]
or
answer3 <- answer2[answer2[,1]!=answer2[,2],]
(which will be much faster than a loop anyway)
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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