Merging is not necessarily an order-preserving operation, but sorting can make
the operation more efficient. The sort=TRUE argument forces the result to be
sorted, but sort=FALSE is in not a promise that order will be preserved. (I
think the imperfect sorting occurs when there are multiple keys but am not
sure.) You can add columns to the input data that let you restore some
semblance of the original ordering afterward, or you can roll your own
possibly-less-efficient merge using match and indexing:
info[ match( grades2$grade, info$grade ), ]
--
Sent from my phone. Please excuse my brevity.
On March 8, 2017 8:07:27 AM PST, Dimitri Liakhovitski
<dimitri.liakhovit...@gmail.com> wrote:
>Hello!
>I have a vector 'grades' and a data frame 'info':
>
>grades2 <- data.frame(grade = c(1,2,2,3,1))
>info <- data.frame(
> grade = 3:1,
> desc = c("Excellent", "Good", "Poor"),
> fail = c(F, F, T)
>)
>
>I want to get the info for all grades I have in info:
>
>This solution resorts everything in the order of column 'grade':
>merge(grades2, info, by = "grade", all.x = T, all.y = F)
>
>Could you please explain why this solution also resorts - despite sort
>= FALSE?
>merge(grades2, info, by = "grade", all.x = T, all.y = F, sort = FALSE)
>
>Thanks a lot!
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