[Rd] data.frame weirdness

[Gabor Grothendieck]

What is going on here?  In the lines ending in #### the inputs and outputs
are identical yet one gives a warning and the other does  not.

a1 <- `rownames<-`(anscombe[1:3, ],  NULL)
a2 <- anscombe[1:3, ]

ix <- 5:8

# input arguments to #### are identical in both cases

identical(stack(a1[ix]), stack(a2[ix]))
## [1] TRUE
identical(a1[-ix], a2[-ix])
## [1] TRUE


res1 <- data.frame(stack(a1[ix]), a1[-ix]) ####
res2 <- data.frame(stack(a2[ix]), a2[-ix]) ####
## Warning message:
## In data.frame(stack(a2[ix]), a2[-ix]) :
##   row names were found from a short variable and have been discarded

# results are identical
identical(res1, res2)
## [1] TRUE


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