[R] unexpected (?) behavior of sort=TRUE in merge function
Rui Barradas
ruipbarradas at sapo.pt
Tue Sep 4 16:57:57 CEST 2012
Hello,
You're right I had missed the point, sorry.
I can't see a reason why that behavior, but it seems to have to do with
all = T, remove it and the problem is gone. But that's probably not what
you want.
NA's issue?
Rui Barradas
Em 04-09-2012 15:17, Meyners, Michael escreveu:
> Rui,
>
> Thanks for looking into this. I apologize, I should've added my output, maybe it looks differently on my machine than on others. I also should have made my question more explicit: I'm not looking for a solution to get the sorting one way or another, I have that already. I rather want to understand why the same code behaves differently on two very similar datasets (one just having less rows, see below).
>
> The first call gives the following for me:
>
>> lapply(test, function(x) merge(x, expand.grid(product=c("Y1", "Y2", "G", "F", "L", "K"), cong=c(-1,0,1,11)), all=T, sort=TRUE))
> [[1]]
> product cong x
> 1 F -1 5.857143
> 2 F 0 3.625000
> 3 F 1 4.782609
> 4 F 11 6.301887
> 5 G -1 7.300000
> 6 G 0 4.800000
> 7 G 1 4.424242
> 8 G 11 5.781250
> 9 K -1 4.375000
> 10 K 0 4.714286
> 11 K 1 3.804348
> 12 K 11 5.566038
> 13 L -1 7.272727
> 14 L 0 6.250000
> 15 L 1 4.875000
> 16 L 11 6.877551
> 17 Y1 -1 5.857143
> 18 Y1 0 3.875000
> 19 Y1 1 3.535714
> 20 Y1 11 5.731707
> 21 Y2 -1 5.900000
> 22 Y2 0 2.500000
> 23 Y2 1 4.638889
> 24 Y2 11 5.419355
>
> [[2]]
> product cong x
> 1 Y1 -1 3.043478
> 2 Y1 0 4.887640
> 3 Y1 1 NA
> 4 Y1 11 NA
> 5 Y2 -1 4.181818
> 6 Y2 0 5.207921
> 7 Y2 1 NA
> 8 Y2 11 NA
> 9 G -1 3.750000
> 10 G 0 5.680000
> 11 G 1 NA
> 12 G 11 NA
> 13 F -1 4.315789
> 14 F 0 5.705263
> 15 F 1 NA
> 16 F 11 NA
> 17 L -1 4.500000
> 18 L 0 6.386364
> 19 L 1 NA
> 20 L 11 NA
> 21 K -1 3.739130
> 22 K 0 4.967033
> 23 K 1 NA
> 24 K 11 NA
>
>
> So different from what you may have observed, here the first data set [[1]] is sorted by label of "product", not by value. As you correctly stated, Y1" is coded as 1, "Y2" as 2, etc., but the first rows are for F, followed by G etc. The second [[2]] is sorted by level (value). So I have different behavior on very similar looking data sets, and hence to me at least one of those cannot be "right" according to documentation (but I agree with you that the second is correct according to the help). In my larger example, it seems as if data sets which do not originally have all combinations of product and cong anyway are sorted like [[2]], and those that are complete (all 24 combinations occur) are sorted like [[1]] is, which to me is still "unexpected".
>
> Hope this clarifies my question.
>
> Any thoughts appreciated.
> Michael
>
>> -----Original Message-----
>> From: Rui Barradas [mailto:ruipbarradas at sapo.pt]
>> Sent: Dienstag, 4. September 2012 14:01
>> To: Meyners, Michael
>> Cc: r-help
>> Subject: Re: [R] unexpected (?) behavior of sort=TRUE in merge function
>>
>> Hello,
>>
>> Inline.
>> Em 04-09-2012 12:24, Meyners, Michael escreveu:
>>
>> All,
>>
>> I realize from the archive that the sort argument in merge has been
>> subject to discussion before, though I couldn't find an explanation for
>> this behavior. I tried to simplify this to (kind of) minimal code from
>> a real example to the following (and I have no doubts that there are
>> smart people around achieving the same with smarter code :-)). I'm
>> running R 2.15.1 64bit under MS Windows 7, full session info below.
>>
>> I do have a list with two dataframes:
>>
>> test <- list(structure(list(product = structure(c(1L, 2L, 3L, 4L, 5L,
>> 6L, 1L, 2L, 3L, 4L, 5L, 6L, 1L, 2L, 3L, 4L, 5L, 6L, 1L, 2L, 3L,
>> 4L, 5L, 6L), .Label = c("Y1", "Y2", "G", "F", "L", "K"), class =
>> "factor"),
>> cong = c(-1, -1, -1, -1, -1, -1, 0, 0, 0, 0, 0, 0, 1, 1,
>> 1, 1, 1, 1, 11, 11, 11, 11, 11, 11), x = c(5.85714285714286,
>> 5.9, 7.3, 5.85714285714286, 7.27272727272727, 4.375, 3.875,
>> 2.5, 4.8, 3.625, 6.25, 4.71428571428571, 3.53571428571429,
>> 4.63888888888889, 4.42424242424242, 4.78260869565217, 4.875,
>> 3.80434782608696, 5.73170731707317, 5.41935483870968, 5.78125,
>> 6.30188679245283, 6.87755102040816, 5.56603773584906)), .Names =
>> c("product",
>> "cong", "x"), row.names = c(NA, -24L), class = "data.frame"),
>> structure(list(product = structure(c(1L, 2L, 3L, 4L, 5L,
>> 6L, 1L, 2L, 3L, 4L, 5L, 6L), .Label = c("Y1", "Y2", "G",
>> "F", "L", "K"), class = "factor"), cong = c(-1, -1, -1, -1,
>> -1, -1, 0, 0, 0, 0, 0, 0), x = c(3.04347826086957,
>> 4.18181818181818,
>> 3.75, 4.31578947368421, 4.5, 3.73913043478261, 4.8876404494382,
>> 5.20792079207921, 5.68, 5.70526315789474, 6.38636363636364,
>> 4.96703296703297)), .Names = c("product", "cong", "x"), row.names =
>> c(NA,
>> -12L), class = "data.frame"))
>>
>>
>> The dataframes are pretty much the same but for the values in the x-
>> column and the fact that the second one has only half as many
>> observations, missing the second half of the expand.grid if you like.
>> Now if I run
>>
>> lapply(test, function(x) merge(x, expand.grid(product=c("Y1", "Y2",
>> "G", "F", "L", "K"), cong=c(-1,0,1,11)), all=T, sort=TRUE)) #
>> sort=TRUE is the default, so could be omitted
>>
>> sorts the first dataframe according to the labels of factor "product"
>>
>> No, it doesn't. It sorts according to the columns, i.e., the values,
>> not according to the labels.
>> The help page clearly states that the argument 'sort' is "logical.
>> Should the results be sorted on the by columns?"
>>
>> And "Y1" is coded as 1, "Y2" as 2, etc. The output is right.
>>
>> Try the following.
>>
>> test2 <- test
>> test2[[1]]$product <- as.character(test[[1]]$product)
>> test2[[2]]$product <- as.character(test[[2]]$product)
>>
>> # To make it more readable.
>> grd <- expand.grid(product=c("Y1", "Y2", "G", "F", "L", "K"), cong=c(-
>> 1,0,1,11))
>>
>> lapply(test2, function(x) merge(x, grd, all=T, sort=TRUE))
>>
>> And now 'product' sorts from "F" to "Y2", even if grd$product is still
>> a factor with the same coding as in 'test'.
>>
>> Hope this helps,
>>
>> Rui Barradas
>>
>> , while for the second one the order is maintained from the first
>> dataframes (x) to merge (which is the difference that I could not find
>> being documented). Now I run the same code with sort=FALSE instead:
>>
>> lapply(test, function(x) merge(x, expand.grid(product=c("Y1", "Y2",
>> "G", "F", "L", "K"), cong=c(-1,0,1,11)), all=T, sort=FALSE))
>>
>> The results are at least consistent and fulfill my needs (this is, btw,
>> not unexpected from the documentation). Note that I get exactly the
>> same behavior if I apply merge subsequently to test[[1]] and test[[2]],
>> so it is not an issue from lapply. (I realize that my dataframes are
>> ordered by levels of product, but using test[[2]] <-
>> test[[2]][sample(12),] and applying the same code as above reveals that
>> indeed no sorting is done but the order is maintained from the first
>> dataframe.)
>>
>> I have a working solution for myself, so I'm not after any advice on
>> how to achieve the sorting -- I'd just like to better understand what's
>> going on here and/or what I might have missed in the documentation or
>> in the list archives.
>>
>> Thanks in advance,
>> Michael
>>
>>
>>
>> Session info:
>> R version 2.15.1 (2012-06-22)
>> Platform: x86_64-pc-mingw32/x64 (64-bit)
>>
>> locale:
>> [1] LC_COLLATE=German_Germany.1252 LC_CTYPE=German_Germany.1252
>> LC_MONETARY=German_Germany.1252 LC_NUMERIC=C
>> LC_TIME=German_Germany.1252
>>
>> attached base packages:
>> [1] stats graphics grDevices utils datasets methods base
>>
>> loaded via a namespace (and not attached):
>> [1] tools_2.15.1
>>
>> ______________________________________________
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>> 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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