[R] Help with getting ?match to not sort

[Peter Alspach]

Tena koe Tal

sort: logical.  Should the results be sorted on the 'by' columns?

Thus it is clear what sort=TRUE does, sort=FALSE does not do this.  That doesn't mean it leaves the result in the same order as x (your a1), although many people (including me at first) assume it does.  It is easy enough to write a wrapper function to retain the order of x in cases like yours.  For example:

mergeRO <- function (x, y, ...) 
{
    myMerge <- merge(cbind(x, myOrder = 1:nrow(x)), y, ...)
    attr(myMerge, "creation time") <- Sys.time()
    myMerge[order(myMerge$myOrder), colnames(myMerge) != "myOrder"]
}

but I'm not sure this will work in all circumstances in which people might use merge().

HTH ...

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Tal Galili
> Sent: Tuesday, 9 November 2010 10:10 a.m.
> To: r-help at r-project.org
> Subject: [R] Help with getting ?match to not sort
> 
> Hello all,
> 
> I think I am missing something about the sorting parameter in the
> "match"
> command/
> Here is an example:
> 
> 
> a1 <- data.frame(name = c("D", "B", "C", "A", "A", "C"))
> a2 <- data.frame(name = c("A", "B", "C", "D"), num = 1:4)
> a1
> a2
> merge(a1, a2, sort = F, by.x = T)
> 
> 
> 
> The result is:
> 
>   name num
> 1    D   4
> 2    B   2
> 3    C   3
> 4    C   3
> 5    A   1
> 6    A   1
> 
> 
> While I wish my rows to be in the same order as in a1, they are having
> some
> other order.
> 
> What am I missing here?
> 
> 
> Thanks.
> 
> 
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