r - Why does reordering turn single column data frames into vectors? -


i curious why reordering single columned data frame (or matrix) converts vector. there reason this?

k <- data.frame(a=c(2,10,3), b=c(8,3,9)) k <- k[order(k[,1]),] class(k) # [1] "data.frame"  k <- data.frame(a=c(2,10,3)) k <- k[order(k[,1]),] class(k) # [1] "numeric"

look @ ?'[' in particular, drop argument

drop: matrices , arrays.  if ‘true’ result coerced       lowest possible dimension (see examples).        works extracting elements, not replacement.  see       ‘drop’ further details.

to answer question, want 

k[order(k[,1]), , drop=false]

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