[R] Subset command and the : operator

From: Chris Beeley <chris.beeley_at_gmail.com>
Date: Fri, 27 May 2011 12:10:36 +0100


Hello-

I have some code that looks like this:

with(mydatalocal, sum(table(Service[Time==5:8])))

This is designed to add up the numbers of responses between the Time codes 5 to 8 (which are integers and refer to quarters). Service is just one of the variables, I'm just trying to count the number of responses so I picked any of the variables. However, there is something wrong, it returns far too low a number for the number of responses. Indeed, if I run this:

with(mydatalocal, sum(table(Service[Time==5|Time==6|Time==7|Time==8])))

I get 4 times as many responses.

I've tried to recreate the problem with the following code:

mydata=data.frame(matrix(c(rep(1, 10), rep(2, 10), rep(3, 10), seq(1, 10, 1), seq(11, 20, 1), seq(21, 30, 1)), ncol=2))

with(mydata, sum(table(X1[X2==9:12])))

with(mydata, sum(table(X1[X2==9|X2==10|X2==11|X2==12])))

but to my immense frustration it actually seems to work fine there, the same number, 4, both times. However, it does generate the following error message:

In X2 == 9:12 :
  longer object length is not a multiple of shorter object length

I know I can use X1[ Time < 9 & Time > 3] but I would like to know what is wrong with the 5:8 usage in case I put it somewhere else and don't notice the problem.

Many thanks!

Chris Beeley
Institute of Mental Health



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 27 May 2011 - 11:14:02 GMT

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