ifelse() has three arguments, named 'test', 'yes', and 'no'.
In both of your two examples, you gave it a test argument of length equal to 1. That is, both length(c())!=0 and length(c())==0 are expressions which when evaluated have length equal to 1.
Therefore, the ifelse() function wants to return an object of length 1. So, it wants to return the first element of either the 'yes' argument, or the 'no' argument, depending on whether test is true or false. But c() has length zero, there is no first element available to return. So you get an error message.
-Don
At 12:12 PM -0600 2/27/04, Svetlana Eden wrote:
Today is a good day for asking question, I guess.
c()NULL[1] TRUE
length(c())==0> r = ifelse(length(c())!=0, c(), c(1,2)) ### OK
r = c() ### OK
r = ifelse(length(c())==0, c(), c(1,2)) ### why this is not OK (given
the previous two)?Error in "[<-"(`*tmp*`, test, value = rep(yes, length = length(ans))[test]) : incompatible typeslogical(0)
c() == NULL
r = ifelse(c()==NULL, c(), c(1,2)) ### why this line does not r ### result in error -logical(0) ### 'c()==NULL' is not TRUE and not FALSE ?
-- Svetlana Eden Biostatistician II School of Medicine Department of Biostatistics Vanderbilt University
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-- -------------------------------------- Don MacQueen Environmental Protection Department Lawrence Livermore National Laboratory Livermore, CA, USA
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