language inconsistency puzzle (in the tradition of Bill V enables (Hi Bill) puzzle "what is x")
R allows you to dynamically extend a vector by assigning past the end. So if a has length 10, then assigning to a[11] creates also a[11] with value a2[11] NA. So a is now length 11, while a2 is still length 10. So the occurrence of a[11] has a different meaning on the assigned-to side than on the assigned-from side. E.g.
a <- rep(1,10) b <- 11 a2 <- a a[b] <- a2[b] a
[1] 1 1 1 1 1 1 1 1 1 1 NA
a2
[1] 1 1 1 1 1 1 1 1 1 1 This doesn't seem inconsistent to me; unavoidable yes, given that you want vectors to be dynamically extendible. Have I missed something? Reid Huntsinger -----Original Message----- From: oehl_list at gmx.de [mailto:oehl_list at gmx.de] Sent: Thursday, November 07, 2002 2:11 PM To: r-help at stat.math.ethz.ch Subject: [R] language inconsistency puzzle (in the tradition of Bill Venables (Hi Bill) puzzle "what is x")
# let's say we have two vectors a and b # lets make a copy of a a2 <- a # not surprisingly identical(a[b], a2[b])
[1] TRUE
# now assigning same to same a[b] <- a2[b] # and SURPRISE identical(a, a2)
[1] FALSE
WHAT IS a AND b ? Hint: this "works" under 1.5.1 and 1.6.1. However, the final value of a will differ between 1.5.1 and 1.6.1 under certain circumstances. Explain why it is both, DOUBLY INCONSISTENT AND UNAVOIDABLE. BTW, the prototype does the same. The serious side of this: I think the situation deserves at least a WARNING. Best Jens Oehlschl?gel
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