Merging problem when column in one DT is factor and in the other character

[Christoph_Jae]

Hi together,

here is the problem I needed dput for: http://www.fileuploadx.de/287440 (sorry, I know that this filehoster is annoying because you have to wait until you can download the file; I hope you have a coffee machine close by ;-)

In this attachment, I basically load in two data.tables DT1 and DT2 that I want to join, i.e. DT2[DT1], according to the keyed columns "Company_Code" and "intDatum" in DT1 and "DSCD" and "intDatum" in DT2. However, while "DSCD" is formatted as a character-column, "Company_Code" is formatted as a factor-column. As you can see from the long structure-object, there are plenty of levels here (the actual data.tables are very small).

Now, when I try to join those with DT2[DT1], I get:

        DSCD intDatum MONTH MV SICClass
 [1,] 997859      151  <NA> NA       44
 [2,] 997859      152  <NA> NA       44
 [3,] 998064      151  <NA> NA       15
 [4,] 998064      152  <NA> NA       15
 [5,] 142268      151  <NA> NA       53
 [6,] 142268      152  <NA> NA       53
 [7,] 142859      151  <NA> NA       56
 [8,] 142859      152  <NA> NA       56
 [9,] 143415      151  <NA> NA       63
[10,] 143415      152  <NA> NA       63
[11,] 307045      151  <NA> NA       15
[12,] 307045      152  <NA> NA       15

Basically, data.table finds no values for MV and MONTH for any DSCD and intDatum combination. However, as DT2[DSCD=="142268"] clearly shows, there are values for that DSCD:

       DSCD      MONTH      MV intDatum
[1,] 142268 1997-08-28 1901.12      151
[2,] 142268 1997-09-28 1829.00      152



Those, however, only show up in the join after i get rid of all the unused levels (equivalently, I can also transform the Company_Code to a character column):



DT1[, Company_Code := factor(Company_Code)]
DT2[DT1]


        DSCD intDatum      MONTH      MV SICClass
 [1,] 997859      151       <NA>      NA       44
 [2,] 997859      152       <NA>      NA       44
 [3,] 998064      151       <NA>      NA       15
 [4,] 998064      152       <NA>      NA       15
 [5,] 142268      151 1997-08-28 1901.12       53
 [6,] 142268      152 1997-09-28 1829.00       53
 [7,] 142859      151       <NA>      NA       56
 [8,] 142859      152       <NA>      NA       56
 [9,] 143415      151       <NA>      NA       63
[10,] 143415      152       <NA>      NA       63
[11,] 307045      151       <NA>      NA       15
[12,] 307045      152       <NA>      NA       15




I'm pretty sure this behaviour occurred only with version 1.8.0, probably because data.table coerced every key to factor before (see the NEWS to 1.8.0). So my question is: Is what happens here intended behavior? I'm honest with you: I'm working now for a while with R and factors are one of those things that I never got. I just don't see their use and every so often they cause me huge problems (as in this case). So I'm probably making something stupid here. The nasty thing about this issue here is that mostly, however, the joins just work as expected (believe me, I tried to produce a simple example with one column factor and one character that would reproduce this behavior, but no matter what I did, the joins afterwards always worked as expected). So in case this is expected behavior, should data.table give at least a warning that says something like "You join two data.tables whereby one keyed column is a factor, one is a character. That is probably not your intention. Convert the factor column to character or vice versa."?





Thanks for your help!



Christoph

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[Matthew Dowle]

Hi. A quick read suggests it's not intended and that's a bug. Just convert
the columns to character for now, and it should work. Character columns
are now preferred going forward, so I'd be suggesting that anyway even if
it worked.

> So in case this is expected behavior, should data.table
> give at least a warning that says something like "You join two
> data.tables whereby one keyed column is a factor, one is a character.
> That is probably not your intention. Convert the factor column to
> character or vice versa."?

Yes. It should be converting to character (with a warning) in this case.
Thought that's what I coded and tested. Will investigate...

> Hi together,
>
> here is the problem I needed dput for: http://www.fileuploadx.de/287440
> (sorry,
> I know that this filehoster is annoying because you have to wait until you
> can download the file; I hope you have a coffee machine close by ;-)
>
> In this attachment, I basically load in two data.tables DT1 and DT2 that I
> want to join, i.e. DT2[DT1], according to the keyed columns "Company_Code"
> and "intDatum" in DT1 and "DSCD" and "intDatum" in DT2. However, while
> "DSCD" is formatted as a character-column, "Company_Code" is formatted as
> a
> factor-column. As you can see from the long structure-object, there are
> plenty of levels here (the actual data.tables are very small).
>
> Now, when I try to join those with DT2[DT1], I get:
>
>
>         DSCD intDatum MONTH MV SICClass
>  [1,] 997859      151  <NA> NA       44
>  [2,] 997859      152  <NA> NA       44
>  [3,] 998064      151  <NA> NA       15
>  [4,] 998064      152  <NA> NA       15
>  [5,] 142268      151  <NA> NA       53
>  [6,] 142268      152  <NA> NA       53
>  [7,] 142859      151  <NA> NA       56
>  [8,] 142859      152  <NA> NA       56
>  [9,] 143415      151  <NA> NA       63
> [10,] 143415      152  <NA> NA       63
> [11,] 307045      151  <NA> NA       15
> [12,] 307045      152  <NA> NA       15
>
>
>
> Basically, data.table finds no values for MV and MONTH for any DSCD
> and intDatum combination. However, as DT2[DSCD=="142268"] clearly
> shows, there are values for that DSCD:
>
>
>
>        DSCD      MONTH      MV intDatum
> [1,] 142268 1997-08-28 1901.12      151
> [2,] 142268 1997-09-28 1829.00      152
>
>
>
> Those, however, only show up in the join after i get rid of all the
> unused levels (equivalently, I can also transform the Company_Code to
> a character column):
>
>
> DT1[, Company_Code := factor(Company_Code)]
> DT2[DT1]
>
>
>         DSCD intDatum      MONTH      MV SICClass
>  [1,] 997859      151       <NA>      NA       44
>  [2,] 997859      152       <NA>      NA       44
>  [3,] 998064      151       <NA>      NA       15
>  [4,] 998064      152       <NA>      NA       15
>  [5,] 142268      151 1997-08-28 1901.12       53
>  [6,] 142268      152 1997-09-28 1829.00       53
>  [7,] 142859      151       <NA>      NA       56
>  [8,] 142859      152       <NA>      NA       56
>  [9,] 143415      151       <NA>      NA       63
> [10,] 143415      152       <NA>      NA       63
> [11,] 307045      151       <NA>      NA       15
> [12,] 307045      152       <NA>      NA       15
>
>
>
> I'm pretty sure this behaviour occurred only with version 1.8.0,
> probably because data.table coerced every key to factor before (see
> the NEWS to 1.8.0). So my question is: Is what happens here intended
> behavior? I'm honest with you: I'm working now for a while with R and
> factors are one of those things that I never got. I just don't see
> their use and every so often they cause me huge problems (as in this
> case). So I'm probably making something stupid here. The nasty thing
> about this issue here is that mostly, however, the joins just work as
> expected (believe me, I tried to produce a simple example with one
> column factor and one character that would reproduce this behavior,
> but no matter what I did, the joins afterwards always worked as
> expected). So in case this is expected behavior, should data.table
> give at least a warning that says something like "You join two
> data.tables whereby one keyed column is a factor, one is a character.
> That is probably not your intention. Convert the factor column to
> character or vice versa."?
>
>
>
> Thanks for your help!
>
>
>
> Christoph
> _______________________________________________
> datatable-help mailing list
> [hidden email]
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help

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[hidden email]
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[Matthew Dowle]

Thanks for example and data, very clear.

Yes, problem looks to be factors with unused levels, when joined to a
character column, as you suggested. Work arounds are to drop the unused
levels or convert to character, as you found.

A fix is a bit more involved and won't have time for a while. Please
could you file a bug report so it doesn't get forgotten.

Thanks.

On Fri, 2012-03-30 at 16:51 +0100, Matthew Dowle wrote:

> Hi. A quick read suggests it's not intended and that's a bug. Just convert
> the columns to character for now, and it should work. Character columns
> are now preferred going forward, so I'd be suggesting that anyway even if
> it worked.
>
> > So in case this is expected behavior, should data.table
> > give at least a warning that says something like "You join two
> > data.tables whereby one keyed column is a factor, one is a character.
> > That is probably not your intention. Convert the factor column to
> > character or vice versa."?
>
> Yes. It should be converting to character (with a warning) in this case.
> Thought that's what I coded and tested. Will investigate...
>
> > Hi together,
> >
> > here is the problem I needed dput for: http://www.fileuploadx.de/287440
> > (sorry,
> > I know that this filehoster is annoying because you have to wait until you
> > can download the file; I hope you have a coffee machine close by ;-)
> >
> > In this attachment, I basically load in two data.tables DT1 and DT2 that I
> > want to join, i.e. DT2[DT1], according to the keyed columns "Company_Code"
> > and "intDatum" in DT1 and "DSCD" and "intDatum" in DT2. However, while
> > "DSCD" is formatted as a character-column, "Company_Code" is formatted as
> > a
> > factor-column. As you can see from the long structure-object, there are
> > plenty of levels here (the actual data.tables are very small).
> >
> > Now, when I try to join those with DT2[DT1], I get:
> >
> >
> >         DSCD intDatum MONTH MV SICClass
> >  [1,] 997859      151  <NA> NA       44
> >  [2,] 997859      152  <NA> NA       44
> >  [3,] 998064      151  <NA> NA       15
> >  [4,] 998064      152  <NA> NA       15
> >  [5,] 142268      151  <NA> NA       53
> >  [6,] 142268      152  <NA> NA       53
> >  [7,] 142859      151  <NA> NA       56
> >  [8,] 142859      152  <NA> NA       56
> >  [9,] 143415      151  <NA> NA       63
> > [10,] 143415      152  <NA> NA       63
> > [11,] 307045      151  <NA> NA       15
> > [12,] 307045      152  <NA> NA       15
> >
> >
> >
> > Basically, data.table finds no values for MV and MONTH for any DSCD
> > and intDatum combination. However, as DT2[DSCD=="142268"] clearly
> > shows, there are values for that DSCD:
> >
> >
> >
> >        DSCD      MONTH      MV intDatum
> > [1,] 142268 1997-08-28 1901.12      151
> > [2,] 142268 1997-09-28 1829.00      152
> >
> >
> >
> > Those, however, only show up in the join after i get rid of all the
> > unused levels (equivalently, I can also transform the Company_Code to
> > a character column):
> >
> >
> > DT1[, Company_Code := factor(Company_Code)]
> > DT2[DT1]
> >
> >
> >         DSCD intDatum      MONTH      MV SICClass
> >  [1,] 997859      151       <NA>      NA       44
> >  [2,] 997859      152       <NA>      NA       44
> >  [3,] 998064      151       <NA>      NA       15
> >  [4,] 998064      152       <NA>      NA       15
> >  [5,] 142268      151 1997-08-28 1901.12       53
> >  [6,] 142268      152 1997-09-28 1829.00       53
> >  [7,] 142859      151       <NA>      NA       56
> >  [8,] 142859      152       <NA>      NA       56
> >  [9,] 143415      151       <NA>      NA       63
> > [10,] 143415      152       <NA>      NA       63
> > [11,] 307045      151       <NA>      NA       15
> > [12,] 307045      152       <NA>      NA       15
> >
> >
> >
> > I'm pretty sure this behaviour occurred only with version 1.8.0,
> > probably because data.table coerced every key to factor before (see
> > the NEWS to 1.8.0). So my question is: Is what happens here intended
> > behavior? I'm honest with you: I'm working now for a while with R and
> > factors are one of those things that I never got. I just don't see
> > their use and every so often they cause me huge problems (as in this
> > case). So I'm probably making something stupid here. The nasty thing
> > about this issue here is that mostly, however, the joins just work as
> > expected (believe me, I tried to produce a simple example with one
> > column factor and one character that would reproduce this behavior,
> > but no matter what I did, the joins afterwards always worked as
> > expected). So in case this is expected behavior, should data.table
> > give at least a warning that says something like "You join two
> > data.tables whereby one keyed column is a factor, one is a character.
> > That is probably not your intention. Convert the factor column to
> > character or vice versa."?
> >
> >
> >
> > Thanks for your help!
> >
> >
> >
> > Christoph
> > _______________________________________________
> > datatable-help mailing list
> > [hidden email]
> > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
>
>
> _______________________________________________
> datatable-help mailing list
> [hidden email]
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help

_______________________________________________
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[hidden email]
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[Christoph_Jae]

I have raised a bug report under, which can be found under #1922.

On Mon, Apr 2, 2012 at 2:17 AM, Matthew Dowle <[hidden email]> wrote:

Thanks for example and data, very clear.

Yes, problem looks to be factors with unused levels, when joined to a
character column, as you suggested. Work arounds are to drop the unused
levels or convert to character, as you found.

A fix is a bit more involved and won't have time for a while. Please
could you file a bug report so it doesn't get forgotten.

Thanks.

On Fri, 2012-03-30 at 16:51 +0100, Matthew Dowle wrote:
> Hi. A quick read suggests it's not intended and that's a bug. Just convert
> the columns to character for now, and it should work. Character columns
> are now preferred going forward, so I'd be suggesting that anyway even if
> it worked.
>
> > So in case this is expected behavior, should data.table
> > give at least a warning that says something like "You join two
> > data.tables whereby one keyed column is a factor, one is a character.
> > That is probably not your intention. Convert the factor column to
> > character or vice versa."?
>
> Yes. It should be converting to character (with a warning) in this case.
> Thought that's what I coded and tested. Will investigate...
>
> > Hi together,
> >
> > here is the problem I needed dput for: http://www.fileuploadx.de/287440
> > (sorry,
> > I know that this filehoster is annoying because you have to wait until you
> > can download the file; I hope you have a coffee machine close by ;-)
> >
> > In this attachment, I basically load in two data.tables DT1 and DT2 that I
> > want to join, i.e. DT2[DT1], according to the keyed columns "Company_Code"
> > and "intDatum" in DT1 and "DSCD" and "intDatum" in DT2. However, while
> > "DSCD" is formatted as a character-column, "Company_Code" is formatted as
> > a
> > factor-column. As you can see from the long structure-object, there are
> > plenty of levels here (the actual data.tables are very small).
> >
> > Now, when I try to join those with DT2[DT1], I get:
> >
> >
> >         DSCD intDatum MONTH MV SICClass
> >  [1,] 997859      151  <NA> NA       44
> >  [2,] 997859      152  <NA> NA       44
> >  [3,] 998064      151  <NA> NA       15
> >  [4,] 998064      152  <NA> NA       15
> >  [5,] 142268      151  <NA> NA       53
> >  [6,] 142268      152  <NA> NA       53
> >  [7,] 142859      151  <NA> NA       56
> >  [8,] 142859      152  <NA> NA       56
> >  [9,] 143415      151  <NA> NA       63
> > [10,] 143415      152  <NA> NA       63
> > [11,] 307045      151  <NA> NA       15
> > [12,] 307045      152  <NA> NA       15
> >
> >
> >
> > Basically, data.table finds no values for MV and MONTH for any DSCD
> > and intDatum combination. However, as DT2[DSCD=="142268"] clearly
> > shows, there are values for that DSCD:
> >
> >
> >
> >        DSCD      MONTH      MV intDatum
> > [1,] 142268 1997-08-28 1901.12      151
> > [2,] 142268 1997-09-28 1829.00      152
> >
> >
> >
> > Those, however, only show up in the join after i get rid of all the
> > unused levels (equivalently, I can also transform the Company_Code to
> > a character column):
> >
> >
> > DT1[, Company_Code := factor(Company_Code)]
> > DT2[DT1]
> >
> >
> >         DSCD intDatum      MONTH      MV SICClass
> >  [1,] 997859      151       <NA>      NA       44
> >  [2,] 997859      152       <NA>      NA       44
> >  [3,] 998064      151       <NA>      NA       15
> >  [4,] 998064      152       <NA>      NA       15
> >  [5,] 142268      151 1997-08-28 1901.12       53
> >  [6,] 142268      152 1997-09-28 1829.00       53
> >  [7,] 142859      151       <NA>      NA       56
> >  [8,] 142859      152       <NA>      NA       56
> >  [9,] 143415      151       <NA>      NA       63
> > [10,] 143415      152       <NA>      NA       63
> > [11,] 307045      151       <NA>      NA       15
> > [12,] 307045      152       <NA>      NA       15
> >
> >
> >
> > I'm pretty sure this behaviour occurred only with version 1.8.0,
> > probably because data.table coerced every key to factor before (see
> > the NEWS to 1.8.0). So my question is: Is what happens here intended
> > behavior? I'm honest with you: I'm working now for a while with R and
> > factors are one of those things that I never got. I just don't see
> > their use and every so often they cause me huge problems (as in this
> > case). So I'm probably making something stupid here. The nasty thing
> > about this issue here is that mostly, however, the joins just work as
> > expected (believe me, I tried to produce a simple example with one
> > column factor and one character that would reproduce this behavior,
> > but no matter what I did, the joins afterwards always worked as
> > expected). So in case this is expected behavior, should data.table
> > give at least a warning that says something like "You join two
> > data.tables whereby one keyed column is a factor, one is a character.
> > That is probably not your intention. Convert the factor column to
> > character or vice versa."?
> >
> >
> >
> > Thanks for your help!
> >
> >
> >
> > Christoph
> > _______________________________________________
> > datatable-help mailing list
> > [hidden email]
> > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
>
>
> _______________________________________________
> datatable-help mailing list
> [hidden email]
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help

_______________________________________________
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[hidden email]
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[Matthew Dowle]

Now fixed in v1.8.1.

On Mon, 2012-04-02 at 13:39 +0200, Christoph Jäckel wrote:

> I have raised a bug report under, which can be found under #1922.
>
> On Mon, Apr 2, 2012 at 2:17 AM, Matthew Dowle <[hidden email]>
> wrote:
>        
>         Thanks for example and data, very clear.
>        
>         Yes, problem looks to be factors with unused levels, when
>         joined to a
>         character column, as you suggested. Work arounds are to drop
>         the unused
>         levels or convert to character, as you found.
>        
>         A fix is a bit more involved and won't have time for a while.
>         Please
>         could you file a bug report so it doesn't get forgotten.
>        
>         Thanks.
>        
>         On Fri, 2012-03-30 at 16:51 +0100, Matthew Dowle wrote:
>         > Hi. A quick read suggests it's not intended and that's a
>         bug. Just convert
>         > the columns to character for now, and it should work.
>         Character columns
>         > are now preferred going forward, so I'd be suggesting that
>         anyway even if
>         > it worked.
>         >
>         > > So in case this is expected behavior, should data.table
>         > > give at least a warning that says something like "You join
>         two
>         > > data.tables whereby one keyed column is a factor, one is a
>         character.
>         > > That is probably not your intention. Convert the factor
>         column to
>         > > character or vice versa."?
>         >
>         > Yes. It should be converting to character (with a warning)
>         in this case.
>         > Thought that's what I coded and tested. Will investigate...
>         >
>         > > Hi together,
>         > >
>         > > here is the problem I needed dput for:
>         http://www.fileuploadx.de/287440
>         > > (sorry,
>         > > I know that this filehoster is annoying because you have
>         to wait until you
>         > > can download the file; I hope you have a coffee machine
>         close by ;-)
>         > >
>         > > In this attachment, I basically load in two data.tables
>         DT1 and DT2 that I
>         > > want to join, i.e. DT2[DT1], according to the keyed
>         columns "Company_Code"
>         > > and "intDatum" in DT1 and "DSCD" and "intDatum" in DT2.
>         However, while
>         > > "DSCD" is formatted as a character-column, "Company_Code"
>         is formatted as
>         > > a
>         > > factor-column. As you can see from the long
>         structure-object, there are
>         > > plenty of levels here (the actual data.tables are very
>         small).
>         > >
>         > > Now, when I try to join those with DT2[DT1], I get:
>         > >
>         > >
>         > >         DSCD intDatum MONTH MV SICClass
>         > >  [1,] 997859      151  <NA> NA       44
>         > >  [2,] 997859      152  <NA> NA       44
>         > >  [3,] 998064      151  <NA> NA       15
>         > >  [4,] 998064      152  <NA> NA       15
>         > >  [5,] 142268      151  <NA> NA       53
>         > >  [6,] 142268      152  <NA> NA       53
>         > >  [7,] 142859      151  <NA> NA       56
>         > >  [8,] 142859      152  <NA> NA       56
>         > >  [9,] 143415      151  <NA> NA       63
>         > > [10,] 143415      152  <NA> NA       63
>         > > [11,] 307045      151  <NA> NA       15
>         > > [12,] 307045      152  <NA> NA       15
>         > >
>         > >
>         > >
>         > > Basically, data.table finds no values for MV and MONTH for
>         any DSCD
>         > > and intDatum combination. However, as DT2[DSCD=="142268"]
>         clearly
>         > > shows, there are values for that DSCD:
>         > >
>         > >
>         > >
>         > >        DSCD      MONTH      MV intDatum
>         > > [1,] 142268 1997-08-28 1901.12      151
>         > > [2,] 142268 1997-09-28 1829.00      152
>         > >
>         > >
>         > >
>         > > Those, however, only show up in the join after i get rid
>         of all the
>         > > unused levels (equivalently, I can also transform the
>         Company_Code to
>         > > a character column):
>         > >
>         > >
>         > > DT1[, Company_Code := factor(Company_Code)]
>         > > DT2[DT1]
>         > >
>         > >
>         > >         DSCD intDatum      MONTH      MV SICClass
>         > >  [1,] 997859      151       <NA>      NA       44
>         > >  [2,] 997859      152       <NA>      NA       44
>         > >  [3,] 998064      151       <NA>      NA       15
>         > >  [4,] 998064      152       <NA>      NA       15
>         > >  [5,] 142268      151 1997-08-28 1901.12       53
>         > >  [6,] 142268      152 1997-09-28 1829.00       53
>         > >  [7,] 142859      151       <NA>      NA       56
>         > >  [8,] 142859      152       <NA>      NA       56
>         > >  [9,] 143415      151       <NA>      NA       63
>         > > [10,] 143415      152       <NA>      NA       63
>         > > [11,] 307045      151       <NA>      NA       15
>         > > [12,] 307045      152       <NA>      NA       15
>         > >
>         > >
>         > >
>         > > I'm pretty sure this behaviour occurred only with version
>         1.8.0,
>         > > probably because data.table coerced every key to factor
>         before (see
>         > > the NEWS to 1.8.0). So my question is: Is what happens
>         here intended
>         > > behavior? I'm honest with you: I'm working now for a while
>         with R and
>         > > factors are one of those things that I never got. I just
>         don't see
>         > > their use and every so often they cause me huge problems
>         (as in this
>         > > case). So I'm probably making something stupid here. The
>         nasty thing
>         > > about this issue here is that mostly, however, the joins
>         just work as
>         > > expected (believe me, I tried to produce a simple example
>         with one
>         > > column factor and one character that would reproduce this
>         behavior,
>         > > but no matter what I did, the joins afterwards always
>         worked as
>         > > expected). So in case this is expected behavior, should
>         data.table
>         > > give at least a warning that says something like "You join
>         two
>         > > data.tables whereby one keyed column is a factor, one is a
>         character.
>         > > That is probably not your intention. Convert the factor
>         column to
>         > > character or vice versa."?
>         > >
>         > >
>         > >
>         > > Thanks for your help!
>         > >
>         > >
>         > >
>         > > Christoph
>         > > _______________________________________________
>         > > datatable-help mailing list
>         > > [hidden email]
>         > >
>         https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
>         >
>         >
>         > _______________________________________________
>         > datatable-help mailing list
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>         >
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>        
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>        
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