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Tal Galili

2010-Nov-08 21:09 UTC

[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.


----------------Contact
Details:-------------------------------------------------------
Contact me: Tal.Galili@gmail.com |  972-52-7275845
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www.r-statistics.com (English)
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jim holtman

2010-Nov-08 21:39 UTC

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[R] Help with getting ?match to not sort

Missing: a closer reading of the help page --

Value
A data frame. The rows are by default lexicographically sorted on the
common columns, but for sort = FALSE are in an unspecified order.

So sort = FALSE says unspecified.  If you want the original order,
then add a column to the dataframe with the order and then sort the
result.

On Mon, Nov 8, 2010 at 4:09 PM, Tal Galili <tal.galili at gmail.com>
wrote:> 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.
>
>
> ----------------Contact
> Details:-------------------------------------------------------
> Contact me: Tal.Galili at gmail.com | ?972-52-7275845
> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
> www.r-statistics.com (English)
>
----------------------------------------------------------------------------------------------
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

Peter Alspach

2010-Nov-08 21:51 UTC

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[R] Help with getting ?match to not sort

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.
> 
> 
> ----------------Contact
> Details:-------------------------------------------------------
> Contact me: Tal.Galili at gmail.com |  972-52-7275845
> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew)
> |
> www.r-statistics.com (English)
> -----------------------------------------------------------------------
> -----------------------
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.
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Phil Spector

2010-Nov-08 22:13 UTC

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[R] Help with getting ?match to not sort

Ted -
    If you want to retain the exact order of the rows of one
of the merged matrices, I think you have to merge them 
"by hand":
> cbind(a1,num=a2[match(a1$name,a2$name),'num'])   name num
1    D   4
2    B   2
3    C   3
4    A   1
5    A   1
6    C   3

 					- Phil Spector
 					 Statistical Computing Facility
 					 Department of Statistics
 					 UC Berkeley
 					 spector at stat.berkeley.edu


On Mon, 8 Nov 2010, Tal Galili wrote:
> 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.
>
>
> ----------------Contact
> Details:-------------------------------------------------------
> Contact me: Tal.Galili at gmail.com |  972-52-7275845
> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
> www.r-statistics.com (English)
>
----------------------------------------------------------------------------------------------
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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